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Minnesota Department of Transportation

S.P. 6918-80, T. H. 53 RELOCATION E-1A Alignment - Embankment VIRGINIA, MN

PRELIMINARY GEOTECHNICAL ENGINEERING REPORT

For

MnDOT

S.P. 6918-80 T.H. 53 Relocation E-1A Alignment - Embankment

in

Virginia, MN

Prepared by

Gale-Tec Engineering, Inc. 801 Twelve Oaks Center Drive

Suite 832 Wayzata, MN 55391

MAY, 2014

GTE Project No. 95443-B

GALE-TEC ENGINEERING, INC. 801 TWELVE OAKS CENTER DRIVE, SUITE 832 WAYZATA, MN 55391 TELEPHONE (952) 473-7193 FAX (952) 473-1492 www.gale-tec.com Ms. Roberta Dwyer, P.E., PTOE May 30, 2014 Minnesota Department of Transportation District Land Management Engineer 1123 Mesaba Avenue Duluth MN 55811 Mr. Gary Person, P.E. Mn/DOT Material & Research Laboratory 1400 Gervais Avenue Maplewood, MN 55101 GTE Project No. 95443-B RE: Geotechnical Engineering Report for S.P 6918-80, T.H. 53 Relocation E-1A Alignment - Embankment in Virginia, MN Dear Ms. Dwyer/Mr. Person: We have completed the geotechnical review of the above referenced project. If you have any questions concerning this report, please do not hesitate to contact us. Respectfully, GALE-TEC ENGINEERING, INC.

Stephan M. Gale, P.E. Nathan M. Lichty, P.E. Barry Christopher, PhD, P.E. Principal Engineer Project Engineer

I hereby certify that this report was prepared by me or under my direct supervision and that I am a Registered Professional Engineer under Minnesota Statute, Sections 326.02 to 326.15.

_________ Stephan M. Gale Date: ___5/30/2014 _____ Reg. No. 13854

NML/SMG REPORT/MnDOT, TH 53, E-1A, Relocation in Virginia, MN

TABLE OF CONTENTS

Page No. EXECUTIVE SUMMARY i 1.0 INTRODUCTION 1

2.0 BACKGROUND 4 2.1 History of Rouchleau Mine Pit 4 2.2 History of Underground Mining in the Area 6 2.3 Bedrock 7 3.0 SUBSURFACE EXPLORATION 7 3.1 Borings 7 3.2 Bathymetric Survey 11 3.3 Geophysical Survey 12 4.0 GLACIAL TILL OVERBURDEN CONDITIONS 13 5.0 SUBMERGED MINE HAUL ROAD EMBANKMENT FILL CONDITIONS 14 6.0 BEDROCK CONDITIONS 17 7.0 ON-SITE GLACIAL TILL CONDITIONS 17 8.0 MINE WASTE ROCK FILL CONDITIONS 17 8.1 General 18 8.2 Gradation and Unit Weight of Mine Waste Rock Fill 18 8.3 Strength Properties of Mine Waste Rock Fill 19 8.4 Settlement Properties of Mine Waste Rock Fill 21 8.5 Summary of Mine Waste Rock Strength and Settlement Parameters 22 9.0 OTHER SOIL/AGGREGATE CONDITIONS 22 9.1 Underwater Fill Conditions 22 9.2 Riprap Fill Conditions 23

10.0 ROUCHLEAU PIT WATER LEVEL CONDITIONS 23 11.0 SEISMIC CONDITIONS DUE TO MINE BLASTING 24 11.1 MnDOT/HDR Mine Blasting Vibration Study 24 11.2 Seismic Force Parameters Inputs for Seismic Embankment Stability Analysis 25

12.0 PROPOSED ROADWAY EMBANKMENT CROSS SECTION 26 12.1 Proposed E-1A Roadway Embankment across Rouchleau Mine Pit 26 12.2 Proposed Roadway Embankment Side Slope Angles 27 12.3 Design Cross Sections 29 12.4 Potential Mine Waste Rock Fill/Bedrock Weakened Interface 30 13.0 PROPOSED ROADWAY EMBANKMENT CONSTRUCTION METHODS 31 13.1 Removal of Vegetation/Debris, Trees and Organic Soils on Submerged Haul Road Embankment Crest prior to Embankment Construction 31 13.2 Embankment Construction in Dry Conditions by Lowering the Water in the Entire 2 Mile Long Series of Mine Pits including the Rouchleau Pit 32 13.3 Embankment Construction in Dry Conditions with Levee-Geotextile Tube Cofferdam and then Construction Zone Dewatering 33 13.4 Embankment Construction (Lower 30 ft) in Wet Conditions with Embankment Fill Placement Into Standing Water 34 13.5 Utilities within Proposed Embankment 35 14.0 ANALYSIS –PROPOSED TH 53 E-1A ROADWAY EMBANKMENT ACROSS ROUCHLEAU PIT 35 14.1 Settlement Analysis of Proposed Embankment 35 14.1.1 Effective Stress Increase due to Embankment Construction 36 14.1.2 Mine Waste Rock Settlement Parameters 37 14.1.3 Geosynthetic Reinforced Embankment Fill Settlement Parameters 37

14.1.4 Settlement Analysis: Design Station 1 Station 6077+00, 100ft Embankment Height 37 14.1.5 Settlement Analysis: Design Station 2, Station 6082+50: 170ft Embankment Height 38 14.1.6 Settlement Analysis: Design Station 3, Station 6090+50: 150ft Embankment Height 38 14.1.7 Settlement Analysis: Design Station 4, Station 6095+00: 135ft Embankment Height 39 14.2 Stability Analysis of Proposed Roadway Embankment 40 14.2.1 Static and Seismic Analysis 41 14.2.2 Monte Carlo Probability Analysis 42 14.2.3 Finite Element Embankment Stability Modeling to Identify Shear Displacement Zones 44 14.2.4 Proposed Roadway Embankment Typical Section 44 14.2.5 Mine Waste Rock Strength Parameters for Analysis 45 14.2.6 Granular Embankment Fill Gradation, Unit Weight and Strength Parameters for Analysis Parameters for Analysis 46 14.2.7 Geosynthetic Reinforcement Properties for Analysis 46 14.2.8 Rouchleau Mine Pit Water Elevation used for Analysis 47 14.3 Stability Analysis of Proposed Roadway Embankment Constructed in the Dry 49 14.3.1 Stability Analysis – Direct Sliding near Reinforced Embankment Base 50 14.3.2 Stability Analysis –Rotational Failure within Reinforced Granular Embankment (Internal Rotation) 53 14.3.3 Stability Analysis – Compound Failure through Both Reinforced Granular Embankment 55 and Mine Waste Rock (Global Stability) 14.3.4 Seismic Stability Evaluation using Monte Carlo Probability Analysis 57 14.3.5 Seismic Stability Evaluation using Shear Displacement Modeling 58

14.4 Submerged Haul Road Embankment Steepened Side Slope Stability 60 14.5 Mine Waste Rock/Bedrock Weakened Interface Stability Analysis 62 15.0 ANALYSIS – EMBANKMENT CONSTRUCTION IN WET CONDITIONS 64 15.1 Material Strength Parameters used in Analysis 65 15.2 Stability Analysis – Station 6095+00, Underwater Fill Placement 65 15.3 Station 6095+00, Underwater Fill Placement, Seismic Stability Evaluation using Monte Carlo Probability Analysis 68 15.4 Summary of Stability Analysis Station 6090+50, Lower 30ft of Embankment Constructed in the Wet without Geosynthetic Reinforcement 69 16.0 ANALYSIS – CONSTRUCTION WITH LEVEE OR GEOTEXTILE TUBE COFFERDAM FOR LOCALIZED DEWATERING 70 16.1 Localized Dewatering Seepage Analysis 70 16.2 Embankment Stability Evaluation associated with Localized Dewatering 72 17.0 RISK REGISTRY AND MITIGATION MEASURES BASED ON INSTRUMENTATION MEASUREMENTS/MONITORING OUTCOMES 72 18.0 RECOMMENDATIONS FOR PROPOSED CLEAR ZONE FROM TOE OF ROADWAY EMBANKMENT TO OUTSIDE EDGE OF EXISTING MINE HAUL ROAD EMBANKMENT 73

19.0 RECOMMENDATIONS FOR DYNAMIC COMPACTION OF EXISTING MINE WASTE ROCK FILL SURFACE 74 20.0 RECOMMENDATIONS FOR BLASTING CRITERIA/RIGHT OF WAY ACQUISITION NEAR PROPOSED EMBANKMENT 76 21.0 RECOMMENDATIONS FOR EMBANKMENT SIDE SLOPE 78 21.1 Roadway Embankment – Constructed in Dry Conditions 78 21.2 Roadway Embankment – Lower 30 ft Constructed in Wet Conditions 79

22.0 RECOMMENDATIONS FOR GEOSYNTHETIC REINFORCEMENT 79

22.1 Material Recommendations 79 22.2 Placement Recommendations 81 23.0 RECOMMENDATIONS FOR 1H:1V AND 1H:1.7V EMBANKMENT SLOPE FACING 82 24.0 RECOMMENDATIONS FOR PREQUALIFICATION EMBANKMENT FILL MATERIAL TESTING 83 25.0 RECOMMENDATIONS FOR EMBANKMENT FILL TESTING DURING CONSTRUCTION 84

26.0 RECOMMENDATIONS FOR UTILITY INSTALLATION IN REINFORCED EMBANKMENT 85 26.1 Encapsulation of Utilities within Concrete Box Culvert or Two Retaining Structures. 85 26.2 Geosynthetic Diversion around Utilities not Encapsulated in a Box Culvert or Between two Retaining Walls 86 27.0 RECOMMENDATIONS FOR ROUCHLEAU PIT DEWATERING FOR EMBANKMENT CONSTRUCTION 87 28.0 RECOMMENDATIONS FOR EMBANKMENT MONITORING DURING/POST CONSTRUCTION 87 29.0 RECOMMENDATIONS FOR FURTHER TESTING AND EVALUATION 89 30.0 RECOMMENDATIONS FOR FUTURE BRIDGE ALONG ALIGNMENT 90 30.1 Future Bridge Installation 90 30.2 Embankment Section to Facilitate Future Bridge Installation 90 30.3 MSE Wall Construction to Facilitate Future Bridge Installation 91 30.4 Recommendations for Future Mine Access Bridge Foundation 92 31.0 PRELIMINARY EMBANKMENT FILL/ GEOSYNTHETIC QUANTITIES 93 32.0 GENERAL QUALIFICATIONS 94

APPENDIX

1. Boring Location Diagram 2. Boring Drill Logs 3. MnDOT Underground Mine Map 4. MnDOT Geophysical Testing Results 5. Embankment Stability Analysis Results 6. Risk Registry 7. Case Histories of Similar Projects 8. References

FIGURES

Figure No. 1: Proposed E-1A Alignment through Southern Portion of the Rouchleau Mine Pit 2 Figure No. 2: Potential E-1A Profile through Rouchleau Mine Pit 3 Figure No. 3: Photo of Rouchleau Mine Pit Taken in 1980’s 6 Figure No. 4: Photo of Rouchleau Mine Pit Taken in 1990’s 6 Figure Nos. 5 & 6: IDEA Drill Rig Drilling off a Barge In Rouchleau Mine Pit 8 Figure No. 7: Locations of Borings along Proposed E-1A Alignment 9 Figure No. 8: Topography of Submerged Haul Road Embankment from MnDOT Bathymetric Survey 12 Figure No. 9: Results of Marine Resistivity Study: Cross Section of Submerged Haul Road Embankment 13 Figure No. 10: Water Depth and Mine Waste Rock Fill Thickness at Boring Locations 16 Figure No. 11: Estimated Mine Waste Rock Gradation based on Mining Methods 18 Figure No. 12: Mine Waste Rock Friction Angle v. Depth for Area beneath Proposed Haul Road Embankment 20 Figure No. 13: Mine Waste Rock Friction Angle v. Depth for Area Outside the Influence of the Proposed Haul Road Embankment 21 Figure No. 14: Embankment Height v. Station for E-1A Roadway Alignment 27 Figure No. 15: Embankment Footprint Width v. Station for E-1A Roadway Alignment 28 Figure No. 16: Results of Monte Carlo Probability Analysis: Factor of Safety Distribution 43 Figure No. 17: FLAC-Slope Modeling with Respect to Embankment Factor of Safety 44 Figure No. 18: Typical 1H:1V Side Slope RSS Embankment Section used in Stability Analysis 45 Figure No. 19: Seepage Analysis No. 1: Station 6082+50 48 Figure No. 20: Seepage Analysis No. 2: Station 6095+00 49

Figure No. 21: Seepage Analysis No. 3: Station 6090+50 49 Figure No. 22: FLAC-Slope Seismic Stability Analysis at Station 6082+50 59 Figure No. 23: FLAC-Slope Seismic Stability Analysis at Station 6095+00 60 Figure No. 24: Submerged Haul Road Embankment Steepened Sideslope Seismic Stability Analysis 62 Figure No. 25: Station 6095+00 Potential Weakened Interface Seismic Stability Analysis, Interface Elevation at 1200ft and terminating 20ft Prior to Slope Face 63 Figure No. 26: Station 6095+00, with Lower Portion of the Embankment Constructed Underwater, Direct Sliding Failure Mode, Seismic Coeff. = 0.3g 68 Figure No. 27: Factor of Safety Gaussian Normal Distribution Calculated from the Monte Carlo Simulation Run No. 6 69 Figure No. 28: Flownet from Seepage Analysis No. 4 72 Figure No. 29: 40ft Embankment Clear zone Between Toe of Reinforced Embankment and Outside Crest of Submerged Mine Haul Road 74 Figure No. 30: Transverse PPA v. Scaled Distance for Blasting Data 77 Figure No. 31: Box Culvert Containing Utilities within Reinforced Embankment 86 Figure No. 32: Utility Conduit within Reinforced Embankment Constructed with MSE and Big Block Wall Faces 86 Figure No. 33: Geogrid Reinforcement Diversion around Horizontal Utility Lines 87 Figure No. 34: Future Bridge Location along Proposed Alignment 91

TABLES

Table No. 1: Summary of Borings performed by IDEA Drilling, Inc. for the E-1A Alignment into the submerged haul road embankment within the Rouchleau Mine Pit 10 Table No. 2: Summary of Borings performed by IDEA Drilling, Inc. for the E-1A Alignment outside of the Rouchleau Mine Pit 11 Table No. 3. Summary of Strength and Settlement Properties of Mine Waste Rock 22

Table No. 4: Stress Increase (Δσ) in Mine Waste Rock Fill beneath Centerline of Proposed Embankment 36 Table No. 5: Calculated Range of Embankment Settlement for Station 6077+00 (100ft Embankment Height) 38 Table No. 6: Calculated Range of Embankment Settlement for Station 6082+50 (170ft Embankment Height) 39 Table No. 7: Calculated Range of Embankment Settlement for Station 6090+50 (150ft Embankment Height) 39 Table No. 8: Calculated Range of Embankment Settlement for Station 6095+00 (135ft Embankment Height) 40 Table No. 9: Minimum Factors of Safety 42 Table No. 10: Monte Carlo Statistical Analysis Input Parameters 43 Table No. 11: Summary of Seepage Analysis Results at Design Cross Sections 48 Table No. 12: Summary of Direct Sliding Failure Mode Analysis at Design Cross Sections 52 Table No. 13: Summary of Internal Rotational Failure Mode Analysis at Design Cross Sections 54 Table No. 14: Summary of Compound Global Stability Failure Mode Analysis at Design Cross Sections 56 Table No. 15: Reinforced Embankment Geosynthetic Requirements at Design Cross Sections 57 Table No. 16: Results of Monte Carlo Seismic Stability Simulations 58 Table No. 17: Results of Station 6095+00 Submerged Haul Road Steepened Sideslope Stability 61 Table No. 18: Monte Carlo Statistical Analysis Input Parameters 65 Table No.19: Summary of Stability Analysis for Lower Portion of Embankment Constructed in Wet Conditions 67 Table No. 20: Result of Monte Carlo Simulation for Station 6095+00, Base of Embankment Constructed in the Wet 69 Table No. 21: Summary of Seepage Flow Rates based on Localized Dewatering 71 Table No. 22: Summary of Scaled Distance Probability Analysis 77 Table No. 23: Minimum Tal for Primary Geosynthetic Reinforcement for

Embankment Construction in the Dry with a Design Seismic Coefficient = 0.3g 80 Table No. 24: Minimum Tal for Primary Geosynthetic Reinforcement for Case where Lower 30ft of Embankment is Constructed into Water and Geosynthetic Reinforcement occurs from 30ft to Top of Embankment, Design Seismic Coefficient = 0.3g 80

Mn/DOT S.P. 6918-80 (TH 53) Relocation - E-1A Alignment - Embankment, Virginia, MN

Gale-Tec Engineering, Inc., May, 2014 i

PRELIMINARY GEOTECHNICAL ENGINEERING REPORT FOR SP 6918-80, TH 53 RELOCATION E-1A ALIGNMENT - EMBANKMENT IN VIRGINIA, MN

EXECUTIVE SUMMARY

Introduction - T.H. 53, extending through the cities of Eveleth and Virginia, MN, requires relocation from its’ existing alignment due to the expiration of a 1960 easement and the subsequent planned expansion of the United Taconite Thunderbird Mine. The E-1A alternative places relocated TH 53 north of the existing roadway alignment through the old Rouchleau Mine Pit that is now partially filled with water). The Rouchleau pit is the southern portion of a series of connected pits that is about 2 miles long north to south and ½ mile wide east to west. Hematite ore was mined from the pit in the 1920-1976 time period by U.S. Steel Corporation. The deepest portion of the pit is 500-600 ft. deep. Old photographs of the pit show that there is an approximate 500 ft wide mine haul road that transects the Rouchleau Pit that is 25-30 ft below the present water surface of 1305 ft (August, 2013). If the new alignment follows this submerged mine haul road across the pit, then the embankment would extend about 2800 lineal ft across the pit; from approximately station 6074+00 to 6102+00. The proposed roadway profile consists of a sag vertical curve with a 4% grade down into the pit and a 4% grade back out of the pit. An embankment height that averages 125 ft and that is as high as 170 ft. above the surface of the submerged mine haul road. The property for the new alignment must be acquired from a private party. The property owner requires that blasting and mining operations be performed near the proposed embankment during construction and adjacent to the embankment at some point in the future. The property owner also requires that one bridge be constructed sometime into the future near the east end of the new alignment and out of the deeper portion of the Rouchleau Pit to allow passage for mining equipment beneath the road once this portion of the mine becomes active. Subsurface Exploration - In 2013 a subsurface exploration within the Rouchleau Pit was performed which included rock borings, a bathymetric survey and a marine electrical resistivity survey. The bathymetric survey identified the submerged mine haul road to be about 500 ft wide at its’ narrowest and at a depth below water (at the time of Aug - Sept. 2013 exploration) of 25-30 ft which results in a mine haul road crest elevation of 1280-1285 ft. The side slopes that form the submerged haul road embankment were estimated to range in height from approximately 80 – 100 ft at about 1.3H:1V (38 degree) slope angles. The marine resistivity survey in conjunction with the borings identified the mine waste rock fill thickness to range from 20-150 ft. A total of twelve (12) rock borings were drilled at select locations along the proposed alignment through the Rouchleau Pit to calibrate the resistivity results regarding the mine waste rock fill thickness and bedrock surface elevation. Drilling through the mine waste rock material was performed with an Exploration Rock Rig by using rotary drilling methods with diamond core drill bits and wireline core barrel sampling techniques. The mine waste rock was found to consist of Cherty and Slaty material from the Biwabik Iron Formation. The mine waste rock fill is estimated to range from sand to boulder size with pieces with typical sizes of 1-2 ft and as large as 6-1/2 ft in diameter.


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Analysis - Previous research and empirical correlation were used to estimate the shear strength and compressibility characteristics of the mine waste rock fill material. In order to limit the embankment footprint to the width of the submerged mine haul road plus a safety margin, the 125 ft wide embankment crest was evaluated with both 1H:1V (45 degree) and a 1H:1.7V (60 degree) side slopes. These relatively steep side slopes will require geosynthetic reinforcement to satisfy static and seismic stability. Embankment settlement and static and seismic stability analyses were performed at four design cross sections along the proposed embankment. The design cross sections were selected based on their unique geometry and differing foundations conditions. The design cross sections include: a location where the proposed roadway embankment will be approximately at it’s greatest height over the submerged haul road embankment (170 ft), a location where the proposed roadway embankment will be present at the narrowest portion of the submerged haul road and adjacent to two (2) 80 -100 ft steep mine haul road slopes, a section where the proposed roadway embankment will be approximately 150 ft in height and a section where the proposed roadway embankment will be constructed with 3H:1V side slopes to facilitate the construction of a future mine access bridge. The static and seismic stability analyses were performed considering a portion of the alignment containing 1H:1V (45 degree) and a portion containing 1H:1.7V (60 degree) geosynthetic reinforced embankment side slopes. The seismic analysis was performed using the data from a HDR Engineering, Inc/Revey and Associates, Inc blast monitoring program conducted in 2012- 2013 and included in a report dated November 18, 2013. We used their data to produce a scaled distance vs transverse peak particle acceleration (PPA) correlation such that we can provide a recommendation regarding a minimum distance from the proposed roadway embankment to future mine blasting locations and such that we can provide a recommendation regarding a maximum charge weight. We incorporated the PPA in the transverse direction from the HDR/Revey report into our seismic stability analysis. The seismic (and not static) analysis was determined to govern the stability design. The results of the seismic analysis indicated that to maintain a minimum factor of safety of 1.1 (recommended by FHWA-NHI-10-025) both an embankment with 1H:1V (45 degree) side slopes and an embankment with 1H:1.7V (60 degree) side slopes would require uniaxial geosynthetic reinforcement (either geogrid or geotextile) with a Long Term Allowable Design Strength (Tal) on the order of 7,000 lbs/ft to 14,000 lbs/ft per FHWA-NHI-10-025; with the geosynthetic reinforcement placed at 1.5 ft to 2.8 ft - 3.0ft vertical increments on both embankment side slopes. The results of the settlement analysis indicate that a total of 2 to 5 ft of settlement is likely to occur within the proposed granular embankment fill and the in-place mine waste rock fill. This settlement will need to be taken into consideration when computing the total quantity of fill required. The assessment also indicates the potential for differential settlement due to the variation in mine waste rock fill thickness beneath the proposed roadway embankment. It is likely that the majority of this settlement will occur during construction. Monitoring will be important to assess settlement performance.


Gale-Tec Engineering, Inc., May, 2014 iii

Recommendations - In general, it would be feasible to construct an embankment along the E-1A alignment extending through the Rouchleau Mine Pit. We recommend that the Rouchleau Mine Pit be dewatered to 6 ft. below the surface of the existing submerged mine haul road and that tree and vegetation removal and grading then occur. The Rouchleau Mine Pit, which is the southern portion of a series of mine pits that have filled with water, is the water body in which the City of Virginia draws its’ drinking water and is the back-up water source for Arcelor Mittal’s Minorca Taconite Processing Plant. A study by HDR Engineering, Inc./Gale-Tec Engineering, Inc. “TH 53 Alternative E-1A Water Management Study” dated March, 2014 has indicated that in order to lower the Rouchleau Pit water level 25-30 ft in a 3 month pumping period, that pumping at a rate of approximately 25,850 gallons per minute would be required. The study indicated that a maintenance pumping rate of 5,400 gallons per minute would be required to maintain the dewatered level. When the new embankment is at least 10 ft above the “normal” water surface of 1305 ft the pumps can be turned off such that the water level would return to its’ “normal” level. Potential receiving water bodies for this dewatering include the West Two Rivers Reservoir, the Arcelor Mittal Enterprise Pit Lake, Sauntry Creek and the US Steel Corporation Tailings Basin-Cell 2. If permitting or some other issue does not allow the transfer of water to these locations to allow construction in the dry, then at least three other options could be considered, though at a higher risk of poor embankment performance. These three options include:

• Construct Retainer Till/Rock Levees into Standing Water, Place Upstream Seepage Reduction System and Dewater Construction Zone - Constructing a till/rock fill retainer levee on each side of the submerged mine haul road by pushing a rock fill into the standing water using a plunging the dozer technique to displace any topsoil that may exist. Old photographs show that trees (½ - 1 ft diameter trunks) exist on the mine haul road. These trees and any other debris would likely need to be removed before the filling operation. These cofferdam levees could then either be incorporated into the final embankment or not. A geomembrane or a geomembrane/clay liner (GCL) composite could be placed on the sides and upstream of the levee to reduce underseepage into the construction zone and then construction zone dewatering could occur. This seepage reduction layer would need to be covered or ballasted down. Once the rock/till levees are in place to a level above the Pit water level and appropriate seepage reduction layers are in place, the pumping of the water from the inside of the cofferdam dike system back over the dike to the Rouchleau Pit could occur. Pump sizes and rates would be a function of the hydraulic conductivity of the upper portion of the mine rock fill and the time allotted for dewatering to be completed. Pump and/or Slug testing of the mine waste rock fill is planned for Spring, 2014 to evaluate the hydraulic conductivity of the mine waste rock fill.

A rock fill levee could be installed on just the north side of the E-1A alignment, with the pumping down of only the southern portion of the Rouchleau Pit.


Gale-Tec Engineering, Inc., May, 2014 iv

• Construct Geotextile Tubes into Standing Water, Place Upstream Seepage Reduction System and Dewater Construction Zone - Levees composed of stacked geotextile tubes (Geotubes ® as termed by one manufacturer) could be deployed on each side of the submerged mine haul road. The tubes would be filled from a slurry box with import sand or fine tailings excavated from one the Mining Companies tailing basins. Based on previous experience, the tubes could be 51 ft in circumference and each tube pumped up to 9 ft high. A 3 - 4 layer stack would be required to achieve a 25 ft height plus 2 – 4 ft of freeboard to allow for wave action and pit water level variation during construction. Geotextile tubes have been used on projects throughout the world since the early 1980’s, often for reclaiming land and water features. Once the geotextile tube levees are in place to a level above the Lake level and the appropriate seepage reduction layer is in place, the pumping of the water from the inside of the geotextile tube system, over the geotextile tube and back into the Rouchleau Pit could occur.

A geotextile tube levee could be installed on just the north side of the E-1A alignment, with the pumping down of the southern portion of the Rouchleau pit. • Construction Lower 30 ft of Embankment in Standing Water – Dredge the trees

and potential topsoil from the submerged haul road embankment area within the embankment footprint and then push a rock type fill into standing water for the lower 30ft of the embankment until embankment fill is above the Rouchleau Pit water level.

Because of the unknown placement techniques for the mine waste rock fill in the 1920 to 1976 time period, we recommend that Dynamic Compaction or some other ground improvement technique be implemented beneath the footprint of the proposed embankment over the Rouchleau Pit submerged mine haul road, provided dewatering is performed. Dynamic compaction is effective in a granular or mine rock type material (not silt or clay) provided the ground water table is at least 6 ft. below grade during dynamic compaction operations. Thus dewatering would need to lower the Rouchleau Pit water level to 6 ft below elevation 1280 ft, or 1274 ft. Where the embankment is constructed over the narrow portion of the submerged haul road, between stations 6089+00 to 6098+50, we recommend that the embankment be constructed with 1H:1.7V (60 degree) side slopes. Between stations 6078+50 and 6089+00 to the eastern side of the embankment and between stations 6098+50 and 6101+00 on the western side of the embankment, we recommend the embankment be constructed with 1H:1V (45 degree) side slopes. These slope angles will provide an approximate 40 ft clear zone between the toe of the proposed reinforced embankment and the edge of the Submerged Mine Haul Road Embankment. Welded Wire baskets in-filled with soil, rock filled gabions, or some facing element, will likely be required to form the 60 degree slope face. The 45 degree slope can be a vegetated face.


Gale-Tec Engineering, Inc., May, 2014 v

A means to generate a cost effective embankment material could be to set up a crushing and screening plant on-site and generate the embankment fill from the existing glacial till overburden material believed to be present in the project cut areas adjacent to the Rouchleau pit. With regard to the proposed embankment fill, we recommend that a study be implemented in order to assess a cost effective gradation for screened and/or crushed on-site fill material. We anticipate screening to a maximum 3 to 4 inch diameter size. We recommend that the angle of internal friction for the reinforced embankment material, as determined by direct shear testing (ASTM D3080), be at least 35 degrees for the material compacted to a minimum of 95 – 98% of the Standard Proctor maximum dry density (AASHTO T-99). We also recommend the fill material contain less than 12% fines. Controls will need to be placed on blasting operations from United Taconite and/or other mining companies that may operate near the embankment. Our review of the available HDR Engineering, Inc./Revey blasting monitoring data from the United Taconite, LLC Thunderbird North Pit suggests that a preliminary blasting guidance include: • Blasting operations within 2000 ft of the proposed embankment toe should be such

that a scaled distance of not less than 13.0 ft/lbs1/2 results. (scaled distance takes into consideration the closest distance between the blast and the toe of the embankment and the charge weight per delay of the blast). Our preliminary statistical analysis indicates that for 13.0 ft/lbs1/2 scaled distance, 95% of the mine blasts will generate a transverse peak particle acceleration (PPA) of less than 0.3g (0.3g was used in our Stability Analysis).

• A maximum charge weight per delay should be established for mine blasting near the embankment, such as 3000 lbs/delay.

• Assuming a maximum charge weight of 3000 lbs/delay, mine blasting should be kept at least 700ft from the embankment toe to maintain a scaled distance of 13.0 ft/lbs1/2.

• Blasting should be directed away from the embankment. Preliminary quantity estimates for that portion of the proposed embankment from Station 6073+50 to 6078+50 at 3H:1V side slopes, from Station 6078+50 to 6089+00 and from Station 6098+50 to 6101+00 at 1H:1V side slopes and from Station 6089+00 to 6098+50 at 1H:1.7V side slopes include: • The dynamic compaction of 105,000 square yards (2300 lineal ft x 400 ft wide) of

surface material, • The screening and/or crushing and placement of about 2.9 million cubic yards plus

settlement compensation of about 186,000 cubic yards of reinforced granular embankment fill material for the 1H:1V and 1H:1.7 embankment side slopes stations (from Station 6078+50 to Station 6101+00),

• The placement of about 3.8 million square yards of primary geosynthetic reinforcement if placed in 3.0ft vertical increments and 1.0 million square yards of secondary geosynthetic reinforcement,


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• The placement of about 0.7 million square yards of Common or Granular Borrow for the 3H:1V side slope embankment between Station 6073+50 to 6078+50.

A bridge for the mine access beneath the embankment is proposed to be installed at some point in the future along the E-1A alignment. The bridge will be located on the eastern portion of the alignment out of the deeper portion of the Rouchleau Mine Pit. We recommend that the portion of the embankment where the future bridge will be located be constructed with 3H:1V unreinforced side slopes to allow for future excavation. Once geosynthetic reinforcement is installed it would be difficult to excavate. One method for reducing excavation requirement when the bridge is built, and thus reducing the 3H:1V side slope embankment section, would be to construct a geotextile wrapped face Mechanically Stabilized Earth (MSE) wall now at the proposed west abutment location at approximately station 6078+50. The wall would be buried during current embankment construction and would eliminate the need for a wide cut out of the embankment during future bridge installation. We estimate about 0.5 million CY of additional Common/Granular Borrow required if the MSE wall method is not implemented.

Potential bridge foundation systems include drilled shaft foundations installed to bedrock, pile foundations installed to bedrock or set in the mine waste rock material, or shallow spread footings bearing on the mine waste rock fill. One method for drilled shaft foundation installation through the mine waste rock fill would be the use of a Cluster Drill. One method for CIP pipe pile installation through the mine waste rock fill could be a down-hole driving (DHD) hammer and Superjaws® overburden drill bits.

There will likely be storm water, sanitary, water and various other utilities placed within the proposed roadway alignment. Due to stability concerns, excavation into the geosynthetic reinforced embankment is not recommended for utility installation or for long-term maintenance. A broken water main, storm or sanitary pipe can also be a potential source for roadway embankment instability. Based on these concerns, we recommend that the utilities be installed within the embankment such that they can be accessed without geosynthetic reinforced embankment excavation and that the reinforced fill is protected in the event of a utility line leak or break. Some options include installation of the utilities within a concrete conduit, creating a reinforced soil sidewall trench and using double lined pipes to reduce the potential for leaks. We recommend that the utilities be installed beneath the Mesabi Trail portion of the embankment. A Risk Registry was completed for the portion of the embankment project proposed to be built over the Submerged Mine Haul Road across the old Rouchleau Mine Pit. This registry defines some of the risks associated with construction of a geosynthetic reinforced embankment constructed over mine waste rock fill material with unknown properties and subjected to seismic forces from mine blasting. The Registry has identified greater risk if construction can not be performed in the dry. The Registry has identified that it will be critical to have knowledgeable engineers on-site during the work, to have a thorough QA/QC program and to have an instrumentation program designed, installed and monitored by experienced engineers as a risk mitigation measure. A risk mitigation plan should be prepared in advance to account for potential occurrences that may be


Gale-Tec Engineering, Inc., May, 2014 vii

indicated by the instrumentation or by observations. The Ralph Peck Observational Method will be an integral aspect of the monitoring for this project. This method includes a process to assess the performance of an earthwork project during construction. The method includes in part:

• Perform general subsurface exploration but not necessarily in detail,

• Assess and analyze favorable and unfavorable conditions,

• Monitor performance

• Have a course of action selected in advance for unfavorable conditions,

• Modify design to suit actual performance.


Gale-Tec Engineering, Inc., May, 2014 1

1.0 INTRODUCTION

T.H. 53, extending through the cities of Eveleth and Virginia, MN, requires relocation from its’ existing alignment due to the expiration of a 1960 easement and the planned mining of the area of land owned by RGGS Land and Minerals and/or MnDNR Permanent School Trust and leased to United Taconite, LLC, a division of Cliffs Natural Resources, Inc. As a result of the 1960 temporary easement agreement and subsequent negotiations with the property owners, the State must either abandon or have the highway relocated by May 5, 2017. As such, Mn/DOT is expecting a bid letting for a potential T.H. 53 E-1A alignment relocation project in Spring/Summer 2015. Mn/DOT is evaluating several route alternatives, including the “E-1A” alternative which places the relocated TH 53 north of the existing roadway alignment through the old Rouchleau Mine Pit. This report addresses the geotechnical engineering issues related to the E-1A alignment and specifically an embankment constructed through the Mine Pit. The Rouchleau Pit and Rouchleau Extension is a connected series of inundated mining pits, located just east of the Virginia city limits. From north to south, these former pits include: the Columbia Pit, the Missabe Mountain Pit, the Shaw-Moose Pit, the Rouchleau Annex Pit, The Rouchleau Pit and the Southern Rouchleau Extension. The Rouchleau and the Rouchleau Extension pits were mined for hematite ore between 1920 and 1976 by U.S. Steel Corporation. Old photographs of the Rouchleau mine pit indicated that a ledge of bedrock was likely left in-place crossing the mine pit from southeast to northwest. This was later confirmed by borings and by a marine resistivity survey. Mine waste rock was placed on the bedrock ledge over an approximately 500ft width to develop a haul road embankment for equipment travel and for a railroad track spur during mining of the Rouchleau Pit. The mine waste rock fill is estimated to be between 20 and 150 ft thick. Photographs taken in the 1980’s and 1990’s (Figure Nos. 4 and 5) show the 500 ft. wide haul road and the adjacent mine pit which extends another 300-400 ft. down to the bottom of the mined pit. Of course, dewatering was required during active mining. When mining activity and dewatering ceased in the 1980’s the water level in the pits rose, submerging the mine waste rock fill haul road embankment. In August, 2013 the water elevation in the pit was reported at 1305.17 ft above mean sea level (MSL). A 2013 bathymetric survey indicate that the top surface of the submerged haul road embankment is approximately 25-30ft below the water surface at an elevation of 1280-1285 ft.



Figure No. 1: Proposed E-1A Alignment through Southern Portion of the Rouchleau Mine Pit

The proposed E-1A alignment has T.H. 53 coming off the existing alignment south of the intersection with TH 135, extending across the old Rouchleau Mine Pit and reconnecting with existing T.H. 53 on the west side of the pit, just west of 2nd Ave W. The roadway is planned to be supported on a constructed embankment, with a section near the east end of the relocated alignment designed to allow for a bridge to be constructed some time in the future so that mining equipment and vehicles can pass beneath the highway when this area is mined. The proposed vertical sag curve profile through the mine pit is shown in Figure No. 2. MnDOT has selected a grade of 4% percent down into the pit and a 4% grade back up. The proposed roadway embankment will be subjected to seismic forces from mine blasting which may be generated near the embankment at sometime into the future. We relied on a report dated November 12, 2013 by HDR Engineering, Inc./Revey & Associates, Inc. and information presented during a “seismic workshop” conducted by HDR/Revey on September 6, 2013 for seismic factors to input into the embankment evaluation.



One construction option is to lower the Rouchleau Pit water level from 1305 ft to 1275 ft. (or about 30 ft) to construct the embankment. After construction, the water level will likely return to its’ preconstruction level. Additionally, the Rouchleau Mine Pit may be dewatered at some time in the future by the mining lease holder to accommodate future taconite mining activities in and around the Rouchleau Pit.

Figure No. 2: Proposed E-1A Embankment Profile through Rouchleau Mine Pit

An embankment crest width of approximately 125 ft is being considered to accommodate four (4) lanes of traffic, the Mesabi Trail and a sound/visual barrier wall. Utilities are planned to be installed below the Mesabi Trail portion of the crest. This preliminary geotechnical evaluation includes 1) a review of the 2013 bathymetric and geophysical surveys performed by or on behalf of MnDOT, 2) a review of the 2013 borings performed by IDEA Drilling on behalf of MnDOT, 3) an assessment of the mine waste rock fill properties by a literature review, 4) the assessment of seismic effects on the proposed embankment by a literature review and by a review of the February 2013 REVEY Associates, Inc./HDR Engineering, Inc. seismic report and an evaluation using scaled distance vs. seismic force correlation, 5) an evaluation and recommendations for a geosynthetic reinforced embankment constructed over the submerged mine haul road embankment extending through the Rouchleau Mine Pit with the lowering of the pit water level prior to and during construction, 6) an evaluation and recommendations for an embankment constructed over the submerged haul road embankment extending through the Rouchleau Pit by constructing a Geotube® or perimeter dike cofferdam and localized dewatering of the construction zone, 7) An evaluation and recommendations and for a

Existing Ground Surface

Proposed Alignment

Southeast Northwest

City of Virginia

Station 6089+00 Station 6102+00 Station 6074+00



construction approach involving placing the lower 30 ft of fill into standing water and then construction of the embankment 8) discussions of ground improvement techniques such as Dynamic Compaction for the existing mine haul road embankment, 9) an evaluation and recommendations for 1H:1V (45 degree) and 1H:1.7V (60 degree) embankment side slopes (resulting in an embankment that will fit on top of the 500 ft. wide submerged haul road embankment, 10) an evaluation of right-of-way limits needed for embankment protection from future blasting 11) a discussion of an instrumentation and monitoring plan, 12) a discussion of a mitigation program based on instrumentation/monitoring outcomes, 13) Preparation of a risk registry and 14) recommendations for a mine access bridge foundation to be constructed near the east end of the realignment at a location to be established sometime in the future (10-20 years). This report was prepared in substantial accordance with the State of Minnesota Professional and Technical Services Agreements 03979 signed June 13, 2013 and 05187 signed January 6, 2014.

2.0 BACKROUND 2.1 History of Rouchleau Open Mine Pit The proposed TH 53 E-1A alignment crosses the southern portion (Rouchleau Mine Pit) of the Missabi Mountain Pit Lake; a series of pits that are about 2 miles long north to south and ½ mile wide east to west. The series of pits are located just east of a residential, commercial and industrial area within the City of Virginia, MN. The southern portion of the current mine pit is named after Mr. Louis Rouchleau, a mining lease holder in this area from the early 1900’s. A photograph from the 1980’s (Figure No. 5) indicates that the mine was excavated to 300-400 ft below the surface on the City of Virginia side of this mine. Hematite ore was mined from the series of pits in the 1920-1976 time period by U.S. Steel Corporation. Mining in the vicinity of the submerged haul road embankment occurred in the 1940 – 1965 time period. It is reported by Skillings Mine Review that 52 million tons of natural ore was mined from the Rouchleau Pit. The Rouchleau Annex Pit (the narrow portion of the pit to the north) was mined (150,000 tons of hematite ore) between 1977 and 1986. At a community project meeting in October, 2013, miners of that era indicated that the 500 ft wide haul road embankment across the middle of the pit was used for railroad cars to access the pit to load out the ore. This was confirmed by US Steel Engineers and by photographs that show the railroad cars and tracks. U.S. Steel Engineers also report that trees up to 6 – 8 inch diameter existed on the haul road prior to it being submerged. Figure Nos. 3 and 4 shows the approximate 500 ft wide haul road embankment prior to it being submerged; with embankment sideslopes of approximately 1.3H:1V. Now the pit has filled with water and the water level in the pit was reported as 1305.17 ft.Mean Sea Level in August, 2013 which was when the bathymetric survey, the geophysical survey and the borings were performed.



Based on the results of the bathymetric survey, the geophysical survey and the borings performed by or on behalf of MnDOT in and around the Rouchleau Pit in 2013, the E-1A alignment was adjusted such that the centerline of the proposed highway embankment was at approximately the same location as the centerline of the submerged mine haul road embankment crossing the Rouchleau Mine Pit. We estimate that the Upper Cherty bedrock was never excavated from beneath this 500ft wide mine haul road embankment. The Upper Cherty bedrock ledge was apparently covered with 20 - 120 ft of mine waste rock fill that was likely placed during mining operations in the time period of 1920-1976 for access of the load-out trains and for other mining equipment and vehicles. The top of the mine waste rock fill over the “ledge” bedrock was approximately 25 ft below the August, 2013 water level (1305.17 ft.) in the pit; with the surface of the mine waste rock fill varying by approximately 5 – 10 ft. After mining of the Rouchleau Mine Pit ceased in the 1980’s, the pit began filling with groundwater and surface run-off. The pit is currently used by the City of Virginia for its’ drinking water source. It is reported that the current water intake was installed in December, 1990 and consists of a horizontal drift into the pit at elevation 1117ft that feeds two vertical shafts extending 200 ft. down into the pit lake. The intake structure is located north of the proposed E-1A alignment. The water is pumped to the City of Virginia Treatment Plant located approximately ½ mile to the west. It was reported that when the Rouchleau Pit was dewatered in 1989-1990 to install the new City of Virginia Intake, that the water was directed to the Wastewater Treatment Plant which then discharged to Manganeka Lake. After dewatering, it is reported that the Rouchleau Pit south of the submerged haul road embankment filled back in slower than the pit on the north side of the submerged haul road embankment. U.S Steel engineers estimated the mine haul road crossing the pit became submerged in 2004. The Accelor Mittal-Minorca ore processing facility, located just to the north, also pumps water from the north end of the Rouchleau Pit. They began periodically pumping in January, 2008 (up to 2000 gpm) from a barge mounted pump station over to their Enterprise Mine Pit Lake. A Northeast Technical Services, Inc. (NTS) report dated May, 2013 reports that the Rouchleau Pit water level had been rising up from 1990 - 2009. As of 2009, NTS reports that because of pumping and other natural events, the lake water level is now expected to drop approximately 175 ft. in elevation (from elevation 1305 ft. to elevation 1117 ft.) over the next 25 years.



Figure No. 3: Photo of Rouchleau Mine Pit Taken in 1980’s

Figure No. 4: Photo of Rouchleau Mine Pit Taken in 1990’s

2.2 History of Underground Mining in the Area A DNR map of documented underground mines in the project vicinity is included in the Appendix. The map indicates that underground mines were located within the proposed embankment construction limits. MnDOT Geology Staff report that comparisons between LIDAR data and drift elevations recorded on the underground mine maps suggest that most of the underground workings in the vicinity of the proposed E-1A embankment were removed during subsequent open pit mining. However, between approximate stations 6073+00 and 6074+00, MnDOT reports a mine drift and several mine slices may be present that plot below current ground surface and thus, may not have been removed during past open pit excavations. MnDOT-Geology reports that glacial till currently forms a talus slope in this area and may compromise the bulk of the subsurface soil thereby rendering the area devoid of workings. However, if underground workings exist, they will not likely be removed during excavation for the 4% roadway profile grade

Submerged Haul Road Embankment

City of Virginia

Submerged Haul Road Embankment

City of Virginia



unless an additional sub-cutting program is prescribed. There is a possibility that undocumented underground workings could exist in this area, particularly where east-west oriented drifts “dead-end” and are not accommodated by adjacent slicing patterns according to MnDOT-Geology. Additional geophysical and drilling investigations could be performed to further assess this issue either now or after the E-1A embankment cut is made. 2.3 Bedrock According to the 2013 rock borings, the mine waste rock fill that overlies the bedrock “ledge” crossing the Rouchleau Mine Pit (beneath the proposed E-1A alignment) consists of the Cherty sub level of the Biwabik Iron Formation. The Biwabik Iron formation consists of four sub layers of iron bearing rock; the Upper and Lower Cherty and the Upper and Lower Slaty. The Cherty sub-members consist of a granular textured rock with individual bedding layers several inches thick while the Slaty layers consist of finer texture and thin individual bedding layers. In stratigraphic order: Upper Slaty, Upper Cherty, Lower Slaty and Lower Cherty.

3.0 SUBSURFACE EXPLORATION 3.1 Borings A subsurface exploration was performed by IDEA Drilling, Inc. (IDEA) in August and September, 2013 on behalf of MnDOT to investigate the glacial till overburden, the mine waste rock fill and the underlying Cherty bedrock that would serve as the foundation for the proposed E-1A roadway embankment. A total of twelve (12) rock borings were performed into the submerged haul road embankment and the Cherty bedrock to identify the interface between the mine waste rock fill and the underlying bedrock. Rock boring locations were selected by MnDOT. These rock borings were performed off a barge as shown in Figure Nos. 5 and 6. Additionally, 11 other rock borings were performed outside of the Rouchleau Mine pit along the E-1A alignment. The rock boring locations are shown on Figure No. 7.



Figure No. 5: IDEA Drill Rig Drilling off a Barge In Rouchleau Mine Pit in September, 2013

Figure No. 6: IDEA Drill Rig/Barge in September, 2013



Figure No. 7: Locations of Borings along Proposed E-1A Alignment

Key: Blue and Green locations are reported to be on RGGS property; Yellow locations are reported to be on MDNR Permanent School Trust property. IDEA cored through the mine waste rock fill and into the underlying Cherty bedrock using rotary drilling methods with diamond core drill bits. IDEA used the same drilling technique to obtain samples of the glacial till soils outside of the mine pit. NQ, HQ and PQ drilling rods and wire line core barrel sampling techniques were used. The borings performed over water from the Barge within the Rouchleau Mine pit were drilled using a Christianson CS 14 drill rig. The borings performed on land in and around the Rouchleau Mine Pit were drilled using Atlas Copco CS 1500, CT14 and CS14c drill rigs. The core bit was advanced though the glacial till overburden, through the mine waste rock fill and into the bedrock by circulating water and drilling fluid mix for cooling and lubrication. A large quantity of water was needed to core the mine waste rock fill within the pit because of the drilling fluid loss into the open matrix of this material. The core barrel sampler was lowered through the hollow drill rod by wire line and advanced by rotating the diamond studded drill bit. When the core barrel sampler was full or plugged with soil or rock pieces, preventing further advancement, then it was retrieved using a winch. The retrieved core was sent to the National Resources Research Institute (NRRI) Coleraine Minerals Lab to be logged. The NRRI logs identify the depth of the mine waste rock fill within the pit, the depth of the glacial till soils outside of the pit and the depth of the bedrock surface at the boring locations. MnDOT obtained the surface elevation of the borings performed on land. A summary of the borings performed through the submerged haul road embankment within the Rouchleau Mine pit is given in Table



No. 1. Table No. 2 summarizes the borings performed outside the pit. Boring logs and a few photographs of the recovery placed in a core box are included in the Appendix. Table No. 1: Summary of Rock Borings performed by IDEA Drilling, Inc. for the E-1A Alignment into the submerged haul road embankment within the Rouchleau Mine Pit

Boring Water Depth (ft) in August, 2013

Ele. of Top of Mine Waste Rock Fill Layer* (ft)

Thickness of Mine Waste Rock Fill Layer

(ft) Elevation of Top of Bedrock* (ft) Northing Easting

31062 24 1281 148 1133 5262569 535885 31069 39 1266 32 1234 5262158 535853 31070 24 1281 41 1240 5262100 535960 31071 24 1281 37 1244 5262031 536060 31072 22 1283 87 1196 5261962 536160 31078 7 1298 109 1189 5262394 535918

31081** 7 1298 5.5 1292 5262317 535789 31082 10 1295 92 1203 5262269 535905 31083 21 1284 122.5 1161 5262215 536014 31084 47 1258 21 1237 5261962 536112 31085 17 1288 91 1197 5261938 535966 31086 15 1290 21 1269 5261870 536068

*Elevation based on a top of water elevation of 1305.17ft. ** Boring Located out of deeper portion of Mine Pit



Table No. 2: Summary of Borings performed by IDEA Drilling, Inc. for the E-1A

Alignment outside of the Rouchleau Mine Pit

Boring

Ground Surface Ele. (ft)

Thickness of Glacial Till

(ft) Elevation of Top of

Bedrock (ft) Bedrock Material Northing Easting

31046 1589.3 20 1569.3 Sandstone 5261237 536292

31047 1585.7 40 1545.7 Pokegama Quartize 5261351 536336

31048 1579.6 48 1531.6 Lower Cherty

from BIF* 5261456 536381

31049 1575.4 72 1503.4 Pokegama Quartize 5261571 536430

31050 - 122 - Lower Cherty

from BIF* - -

31051 1571 120 1451 Pokegama Quartize 5261679 536489

31066 1486.5 22 1464.5 Upper Cherty

from BIF* 5262210 535517

31067 1492 34 1458 Upper Cherty

from BIF* 5262194 535610

31068 1499.6 33 1466.6 Upper Cherty

from BIF* 5262219 535705

31074 1315 Not Yet Logged 5261872 536285

31080 1505.1 24 1481.1 Upper Cherty from BIF* 5262371.6 535651.5

*BIF = Biwabik Iron Formation - Not Obtained 3.2 Bathymetric Survey In July, 2013 MnDOT performed a bathymetric survey of the southern portion of the Rouchleau mine pit, including the submerged haul road embankment beneath the proposed E-1A alignment. Depths were measured using an Odom Hydrotrac and Odom Echotrac CV100 depthsounders. GPS coordinates were measured using a Trimble GeoExplorer6000. These GPS and depthsounder readings created a topographical map of the pit accurate up to about 4 inches, according to MnDOT. The results of the bathymetric survey indicate that the submerged haul road embankment crest is approximately 500ft wide at its’ narrowest location and has a surface elevation ranging from 1280 – 1290ft. The results of the survey also indicate the submerged haul road embankment has steepened sideslopes located on both the north and south sides of the submerged haul road embankment as shown in Figure No. 8. The survey indicates that these steepened slopes are approximately 60 – 80ft in height and are at a slope angle



of approximately 1.3H:1V (38 degrees). Figure No. 8 shows the results of the bathymetric survey for the submerged haul road embankment.

Figure No. 8: Topography of Submerged Haul Road Embankment from MnDOT

Bathymetric Survey

3.3 Geophysical Survey A towed marine electrical resistivity survey was performed on July 10, 2013 by MnDOT and Carr Geophysical Consulting. The survey was performed within the southern portion of the Rouchleau Mine Pit and over the submerged haul road embankment. This survey was performed prior to the rock borings being drilled to gain an understanding of the material comprising the submerged haul road embankment and to assist in locating rock borings. Geophysical data was collected using an 8-channel SuperSting R8/56+ electrical resistivity meter and a 56-electrode stationary underwater cable which were both manufactured by Advanced Geosciences, Inc (AGI). Depth, GPS and water temperature measurements were collected via Lowrance HDS5 depth finder and were synchronized with the resistivity measurements during pre-processing using AGI’s Marine Log Manager software. All data was processed using AGI’s EarthImager software and supplemental Continuous Resistivity Profiling module.

Submerged Haul Road Embankment Steep Sideslopes

Haul Road Embankment Area

Proposed Highway Centerlines



A roughly 600-foot underwater resistivity cable was towed around the pit and behind a boat traveling about 2 to 3 mph. A weaving tow pattern was used along with a dipole-dipole array to provide adequate electrical depth coverage of the E-1A alignment. During each current injection, conductivity measurements were obtained at varying locations along the cable on all 8 resistivity meter channels. The field geometry and array ultimately provided processed profile depths of around 140 feet below water surface. Cross sections of the submerged haul road embankment were developed from the resistivity results. These cross sections indicate that the submerged haul road embankment consists of a surface layer of boulders, cobbles and gravel material (mine waste rock fill) overlying bedrock. The mine waste rock fill (blue and green in Figure No. 9) thickness varies between approximately 40ft and 120ft within the embankment. There also appears to be several dramatic changes in bedrock (yellow and red in Figure No. 9) elevations across the approximately 500ft wide embankment, with several bedrock peaks and valleys. The resistivity difference may, however, be a waste rock fill that was placed at a different date with different properties. A cross section of the submerged haul road embankment is shown in Figure No. 9. Additional cross sections are provided in the Appendix. Figure No. 9: Results of Line 7 - Marine Resistivity Study: Cross Section of Submerged

Haul Road Embankment

The figure above (Line No. 7) shows a sloping bedrock surface which could be a potential plane of weakness. This case was evaluated (See Report Section 14.5).

4.0 GLACIAL TILL OVERBURDEN CONDITIONS

Glacial till deposits are located outside of the Rouchleau Mine pit in the proposed cut areas for the proposed TH 53 realignment. This material is a likely source for embankment fill for the proposed roadway embankment. According to the Minnesota Geological Survey, Geologic Atlas for St. Louis County, the Glacial Till in the Virginia-Mountain Iron Area generally consists of loamy sands with some cobble and boulder size particles generally consisting of less than 10 % of the soil matrix The Geologic Atlas indicates that these deposits may be up to 60ft thick in some areas. Cotter and Rodgers (1961) report that the Oliver Iron Mining Division of U.S. Steel Corporation permitted USGS geologists to observe drilling of 68 holes in the northern portion of Virginia in the



1950’s. They reported that much of the area was covered by very permeable sands and gravels. These glacial till soils were deposited during the last glacial retreat from northeastern Minnesota approximately 10,000 years ago. Soil borings are presently being performed in these areas. The results were not available at the time this report was prepared.

5.0 SUBMERGED MINE HAUL ROAD EMBANKMENT FILL

CONDITIONS

The results of the bathymetric survey, the marine resistivity survey and the rock borings indicate that the top of the submerged haul road embankment varies in elevation from about 1280 – 1290ft along the E-1A alignment. As of August, 2013 the water level in the Rouchleau Mine Pit was at an elevation of 1305.1 ft; thus the haul road embankment was submerged by approximately 15 – 25ft. Rock borings (31069 and 31084) performed near the edges of the submerged mine haul road indicate deeper water depths, approximately 40 – 50ft deep at these locations. Figure No. 11 shows the water depth and mine waste rock fill thickness at the boring locations based on a top of water elevation of 1305.1ft. The rock borings performed through the submerged mine waste rock fill indicate the mine waste rock thickness varies from between approximately 20 to 120ft thick along the proposed alignment. The rock borings performed along the southern portion of the submerged mine haul road embankment (borings 31069, 31070, 31071, 31085 and 31086) indicate a mine waste rock thickness of between 20ft and 40ft, while the borings performed on the northern portion of the submerged haul road embankment (borings 31078, 31081, 31082 and 31083) indicate a mine waste rock thickness of between 75 and 122ft. The mine waste rock fill thickness generally increases by about 40 to 50ft along the northern and northwest portions of the submerged mine haul road embankment. The bathymetric survey and borings identify that this submerged mine haul road embankment: • Is approximately 500 ft. wide at one of the narrow cross sections, • Is bound by 60ft to 80ft high steep slopes on both the Northwest and Southeast sides • Is at a crest elevation of 1280 – 1290ft, or approximately 15-25 ft. down below the

August, 2013 Mine Pit water surface of 1305.17 ft. The mine haul road crest elevation varies by approximately 5 – 10 ft.

• Consists of approximately 20-120 ft. of mine waste rock fill over Upper Cherty bedrock.

The existing submerged haul road embankment consists of previously excavated mine waste rock fill material from within the Rouchleau Mine. Based on the results of the borings, this material consists of quarried/blasted Upper Cherty material ranging in size from boulders to sand sized. Based on the review of old aerial photos, the submerged haul road embankment served as an access road and rail spur into and out of the Rouchleau Pit for mining equipment and railcars. It is likely that it was progressively constructed during active mining to facilitate Rouchleau Pit expansion. US Steel



Corporation cross sections of the mine haul road embankment show that the embankment was built in the 1960’s and was completed in 1971. These sections are on-file with MnDOT Geology. The submerged haul road embankment, as it exists today, consists of an approximately 500 – 600ft wide embankment crest with 60-80ft high embankment side slopes estimated to be at an approximately 1.3H:1V slope down to the next mining level in the pit (See Figure No. 3). This “mine dump” was likely placed with large (D-10) dozers which tracked over the dumped material to provide compaction and thus reduced the potential for settlement and edge failures. During active mining, blasting likely occurred within 1000ft and probably closer to the submerged haul road embankment. Similar access roads, constructed to heights of a few hundred feet high and consisting of similar material have been constructed within or adjacent to past mining pits on the Iron Range, and most have remained stable. Minnesota Rules, Chapter 6130 on Ferrous Metallic Mineral Mining requires reclamation of mine rock stockpiles. This regulation went into effect in August, 1980. Mineland Reclamation Rule 6130.2400 “Standards for Rock, Lean Ore and Coarse Tailings Stockpiles” has standards for construction. This standard includes a statement that “final exterior slopes be no more than 30ft to 40ft high, and no steeper than the angle of repose”. Rule 6130.2500 states that “a minimum of two feet of surface overburden shall be placed upon the completed portions of each bench and top of any rock, lean ore and coarse tailings stockpile.” Thus we suspect a soil cover was placed on the embankment and then it was vegetated, as shown in Figure No. 4. Rule 6130.3900 also includes requirements for blasting. The present requirement is that the permittee (mine) shall limit the peak particle velocity to 1 inch/second (in/s) and limit the air overburden pressure when blasting near structures located outside the Permit to Mine area.



Figure No. 10: Water Depth and Mine Waste Rock Fill Thickness at Boring Locations

*Water Depth based on August, 2013 Water Surface Elevation of 1305.1ft

Water Depth = 7ft Mine Waste Rock Thickness = 109ft

Water Depth = 7ft Mine Waste Rock Thickness =5ft











6.0 BEDROCK CONDITIONS

The NRRI core logs identify that the bedrock surface within the existing Rouchleau mine pit beneath the proposed E-1A embankment consists of the Lower Cherty sublayer from the Biwabik Iron Formation. This rock type was encountered at all boring locations within the Rouchleau Pit beneath the proposed embankment. Outside the pit, Sandstone and Pokegama Quartize were also encountered.

7.0 ON-SITE GLACIAL TILL CONDITIONS

The proposed E-1A alignment roadway profile will include an approximately 40ft cut on the west (Virginia) side and an approximately 70ft cut on the east (Gilbert) side of the Rouchleau mine pit as shown in Figure No. 2. The IDEA drill core recovery represented by NRRI boring logs and photographs of the recovery within core boxes identify this material to be a glacial till consisting of boulders, cobbles, gravel, sand and silt size particles. Glacial geology of the area also suggests this soil type. The borings indicate that the glacial till material extends to a depth of approximately 180ft on the east (Gilbert) side of the mine pit and to a depth of approximately 30ft on the west (Virginia) side of the mine pit. In most cases, Cherty bedrock was encountered beneath the glacial till. Potential on-site TH 53 E-1A embankment fill will include excavated glacial till, blasted/excavated Cherty bedrock and the reuse of mine waste rock fill available from cut areas. Borings were being performed in these areas at the time this report was prepared. This on-site glacial till will be a likely source for embankment fill. Because of the suspected fines content variation and the larger gravel size particles, we anticipate that this material can be crushed and/or screened and if need be washed to process an acceptable material for use with geosynthetic reinforcement. We estimate a compacted dry density of potential glacial till fill to be 125 lbs/ft3 (pcf). We estimate a drained friction angle residual of 35 degrees per ASTM D-3080 for a processed glacial till compacted to 95 to 98% of the maximum dry density. We recommend a testing program be implemented to further define these properties before an embankment design is finalized. Recommendations for additional prequalification testing are in Section 23.0 of this report.

8.0 MINE WASTE ROCK FILL CONDITIONS

The support for the proposed TH 53 E-1A embankment through the Rouchleau Mine Pit consists of approximately 20 - 120 ft of a mine waste rock fill overlying Lower Cherty bedrock. The mine waste rock fill thickness averages about 35ft on the southern and eastern portions of the submerged mine haul road embankment within the Rouchleau pit and increases to a thickness of about 120ft in the northwest portion of the proposed alignment within the Rouchleau Mine Pit.



8.1 General Due to the size and composition of the mine waste rock fill, representative field samples could not be obtained with the rock drilling procedure utilized by IDEA. Thus samples could not be recovered for laboratory testing to obtain gradation, strength and settlement properties of the mine waste rock fill. The strength and settlement properties of the mine waste rock fill were estimated based on a published literature review and the development of empirical correlations by others. Cross hole seismic testing of the in-place mine waste rock fill is proposed in 2014. The seismic cross hole method (ASTM D-4428) will potentially provide information pertinent to the seismic wave velocities of the mine waste rock fill, which can be used to assess anomalies that might exist between boreholes. A discussion of recommended additional testing is included in Section 28 of this report. 8.2 Gradation and Unit Weight of Mine Waste Rock Fill It is likely that the mine waste rock fill generated in the 1920 - 1976 time period and placed for the approximate 500 ft. wide submerged haul road embankment, which crosses the Rouchleau Mine Pit, was blasted/excavated Cherty bedrock with a gradation that is likely similar to the mine waste rock fill stockpiles exposed for the Auburn Mine Pit (a UTAC pit nearby the Rouchleau Pit). Revey, 2013 estimated the gradation of the Auburn Mine Pit waste rock based on rock strength and blasting charge weight. Blasting charge weights were not available for the 1920 – 1976 time period from U.S. Steel Corporation. The resulting gradation is giving in Figure No. 11. These results indicated an average particle size (D50) of about 1ft and an estimated maximum particle size of about 6 ½ ft. This size range is corroborated by our observations of the Auburn Pit Stockpiles.

Figure No. 11: Estimated Mine Waste Rock Gradation based on Mining Methods



A specific gravity of 4.1 was estimated for the Cherty sublayer of the Biwabik Iron Formation. A porosity of 30% is typically used to assess the volume of riprap or rock fill. Using these values, the density of the mine waste rock was estimated to be 180 lbs/ft3 (pcf). 8.3 Strength Properties of Mine Waste Rock Fill Barton and Kjaernsli (1981) indicate that the shear strength of rock fill can be estimated empirically by determining the equivalent strength of the rock pieces and the equivalent roughness of the particles. These two (2) parameters can be used to empirically estimate the angle of internal friction between boulders in rock fill as shown in Equation 1. φ' = Rlog(S/σ’n) + φb (Equation 1) Where: φ' = the angle of friction of the rock fill material R = equivalent roughness of the rock fill S = equivalent rock fill strength σ’n = effective normal stress

φb = residual angle of friction between particles The equivalent roughness (R) can be estimated by determining the degree of particle roundness and also the porosity of the rock material (n). The degree of particles roundness of the mine waste rock has been described by visual observation as sharp and angular with rough surfaces, which is typical for quarried Cherty and Slaty rock. The porosity of the mine waste rock is estimated between 20% – 30%. Based on these observations, a chart presented by Barton and Kjaernsli indicates an equivalent roughness value of about 7 or 8. The equivalent strength (S) can be determined by the average rock particles size (d50) and the unconfined compressive strength (σ’c) of the rock fill. The unconfined compressive strength of the rock fill particles was estimated from testing performed by Carranza-Torres (2009). In this laboratory study, the density (γ) and unconfined compressive strength (σ’c) of samples from four (4) layers of the Biwabik Iron Formation were determined from the rebound hammer method (ASTM D5873). The results of this testing indicated an average density of about 190 pcf and an average unconfined compressive strength of about 29 ksi for the Cherty rock. Based on these estimates of the unconfined compressive strength and the average particles size and using a figure presented by Barton and Kjaernsli, the equivalent rock fill strength (S) was estimated at 1x106 pounds per square foot (psf). Barton and Kjaernsli indicate that as the effective stress acting on the rock fill increases, the overall friction angle tends to decrease due to cracking and particle breaks along contact interfaces. Using these principles, charts were developed to estimate the angle of internal friction of the mine waste rock material based of a varying equivalent roughness and subjected to various effective stresses, both beneath and outside the influence of the proposed TH 53



roadway embankment. The angle of internal friction of the mine waste rock fill beneath the proposed TH 53 roadway embankment will be less than the angle of internal friction of the mine waste rock fill outside of the embankment footprint, due to the effective stress increase caused by embankment fill. The stress increase created by the proposed TH 53 roadway embankment fill was used to estimate the reduction of the angle of internal friction for the mine waste rock fill beneath the proposed roadway embankment. The charts are given as Figure No. 12 and Figure No. 13. Figure No. 12: Mine Waste Rock Fill Friction Angle v. Depth for Area beneath Proposed

TH 53 Roadway Embankment Footprint

Mine Waste Rock Frictio Angle v. Depth (after Stress Increase From Embankment Fill (170ft))

41

42

43

44

45

46

47

48

49

0 10 20 30 40 50 60 70 80 90 100 110

Depth (ft)

Friction

Angle (P

hi) R = 8

R = 8.5

R=9

R=9.5

R=10

R=10.5

R = 11



Figure No. 13: Mine Waste Rock Fill Friction Angle v. Depth for Area Outside the Influence of the Proposed TH 53 Roadway Embankment

Mine Waste Rock Fill Friction Angle v. Depth (no overburden pressure)

4445464748495051525354555657585960

0 10 20 30 40 50 60 70 80 90 100 110

Depth (ft)

Friction

Angle (phi)

R = 8 R = 8.5 R=9 R = 9.5 R = 10 R = 10.5 R = 11

The results, shown in Figure Nos. 12 and 13, indicate a reduction in friction angle with depth beneath the submerged haul road. These results were used in the stability analysis. For the area beneath the proposed roadway embankment, the friction angle is estimated to range from 48.3 to 41.9 degrees, depending on the equivalent roughness of the material. With a constant equivalent roughness value, the mine waste rock friction angle is reduced by a value of 0.2 degrees for every 10ft in depth due to the effective stress increase. For the area outside the influence of the roadway embankment, the friction angle could range from 60 degrees near the ground surface, to a value of 44 degrees at a depth of 110ft. 8.4 Settlement Properties of Mine Waste Rock Fill Published literature pertaining to rock fill settlement (Fitzpatrick, 1985 and Hunter & Fell, 2002) expresses the settlement of the crest of rock fill dams and mine waste fills as a function of their self-weight. The settlement from the self weight of the mine waste rock fill mass within the submerged mine haul road embankment has likely already occurred since the submerged mine haul road embankment has been in place for at least 40 years. The mine waste rock fill is expected to compress due to the load applied by the proposed 130 – 170 ft high TH 53 roadway embankment. Settlement should occur during the load application (during the approximate 1 to 1½ year construction period). The settlement is expected to be a function of the elastic modulus of the rock fill. Fitzpatrick (1985) presented a means to determine the elastic modulus of rock fill based on the settlement observed during construction of a rock fill dam. The method for estimating the elastic modulus (E) of rock fill material by Fitzpatrick (1985) is given in Equation 2.

Mine Waste Rock Fill Friction Angle v. Depth (No Stress Increase from Embankment Fill)



Erf = σn(Drf/δrf) (Equation 2)

Where: Erf = Elastic Modulus of the rock fill in psf σn = normal stress applied, typically = γH where γ is the density of the fill material in lbs/ft3 and H is the height of the fill placed in feet Drf = total thickness of rock fill in feet δrf = strain = settlement of rock fill over Drf

Using this method of analysis, Hunter & Fell (2002) back calculated a static modulus of rock fill based on observed settlement of rock fill dams constructed with varied construction methods and materials. It is likely that the mine waste rock fill was placed for the submerged haul road embankment within the Rouchleau Mine Pit with 40 – 80ft high mining benches. The mine waste rock fill has been submerged since 2004 due to the rising water level in the in-active mine pit. This submergence reduces the effective stress acting on the mine waste rock and also lubricates the interfaces between adjacent particles in the mine waste rock matrix. Submergence may increase the potential for movement between individual particle interfaces, thus causing increased settlement as compared to an embankment above water. Case studies presented by Hunter & Fell based on similar rock strength, gradation, and placement conditions and final submerged conditions indicate elastic modulus limits for the proposed TH 53 embankment between 15 MPa (310,000 psf) and 20 MPa (418,000 psf). 8.5 Summary of Mine Waste Rock Fill Strength and Settlement Parameters

Table No. 3. Summary of Strength and Settlement Properties of Mine Waste Rock

Property Unit Weight (pcf)

Angle of Internal Friction (φ) (degrees)

Elastic Modulus (E) (psf)

Range of Values 180 – 200 pcf 41.5o – 60o 310,000 to 418,000

9.0 OTHER SOIL/AGGREGATE CONDITIONS

9.1 Underwater Fill Conditions If the Rouchleau Mine Pit is not dewatered to facilitate reinforced embankment construction in the dry, then the lower 25ft of the proposed roadway embankment, approximately from elevation 1280ft to 1305ft, will have to be constructed underwater. Fill material placed into standing water will not be able to be reinforced with geosynthetic reinforcement and it will likely be difficult to obtain the compaction standards typically required for fill placement of embankments. We estimate that a clean,



uniformly graded gravel or crushed rock fill material would need to be used for the underwater fill material. We estimate a dry density of underwater fill to be 120 lbs/ft3. We estimate a drained friction angle of 30 degrees for this material unless some level of densification can be achieved during placement (i.e. vibro induced methods). We recommend a testing program be implemented to further define these properties, if this approach is to be considered. Recommendations for additional testing are in Section 23.0 of this report. 9.2 Riprap Fill Conditions ume the rip rap fill would consist of blasted/excavated bedrock material, as well as bo An aggregate slope face/riprap is proposed for the submerged portions of the 1H:1V (45 degree) and the 1H:1.7V (60 degree) embankment side slopes. The aggregate/riprap will likely have characteristics (density, angularity, degree of particle roundness, etc.) similar to existing mine waste rock fill material. Therefore, the aggregate/riprap strength parameters were assumed to be the same as the mine waste rock fill material that comprises the submerged haul road embankment, a density of 180 pcf and an angle of internal friction of 50 degrees. These values should be further investigated and refined for final design.

10.0 ROUCHLEAU PIT WATER LEVEL CONDITIONS The water level in the Rouchleau Pit will need to be lowered, or at least within the construction zone, if the embankment construction across the Pit is to occur in the dry. The Rouchleau Pit and Rouchleau Extension are the southern open mining pits within a series of pits that run 2 miles north to south along the eastern side of the City of Virginia. These two pits are divided by a bedrock ledge with mine rock fill placed over the bedrock. This mine rock fill /bedrock ledge has a surface elevation of about 1280 ft per the bathymetric survey. When mining activity and dewatering ceased in the 1980’s, the water level in the pit rose. Water levels fluctuated between elevation 1115 ft and 1135 ft in the 1980’s. Starting in the early 1990’s, the water level in the pit began to rise. Water elevations of 1225 ft and 1310 ft are reported for 1997 and 2009, respectively. We suspect the mine haul road became submerged in 2003/2004. During September, 2013 the water elevation in the pit lake was 1305 ft, or approximately 25 ft above the mine rock fill surface. The Rouchleau Pit water level is affected by pumping by the City of Virginia for municipal water supply and by ArcelorMittal to maintain the water level in their nearby Sauntry/Enterprise Pit. The most-recent historic high water elevation in the Rouchleau pit was 1310 ft in December, 2009 (NTS, 2013). In 2011, the City of Virginia pumped an average of 1,974 gpm from the series of Pits associated with the Rouchleau Pit. Arcelor Mittal pumped an average of 1,215 gpm from the Pits in 2012 (HDR, 2014). MnDNR Water Appropriation Permit No. 1984-2037 allows the City of Virginia to withdraw up to 4,000 gpm or nor more than 1 billion gallons per year from the series of



Pits on the east side of Virginia. NTS, 2013 reports that if the pumping rate exceeds 2,350 gpm in a typical year, then the water level will decline. Additionally, future mining plans by United Taconite or others who may mine the area in the future may result in the pit being dewatered once again so that open cut mining of taconite could occur sometime in the future. HDR (2014) reports that if all pumping from the pit ceases, that the water level could conceivably return to a City of Virginia well reading of 1396 ft in Nov. 1996 or 1428 ft in June 1982.

11.0 SEISMIC CONDITIONS DUE TO MINE BLASTING The relocated E-1A alignment will be within the future taconite mining area, though it is reported that there are no reserves beneath the proposed embankment footprint. The mining of taconite ore will be ongoing at the United Taconite LLC (UTAC) Thunderbird North mining property during TH 53 roadway embankment construction (about 2000ft away) and into 2017 when the new relocated TH 53 is opened. UTAC proposes to mine taconite ore out of the area in and around the Rouchleau Pit some time after 2017. The Rouchleau Pit was previously mined for hematite ore. UTAC and other mining companies on the Iron Range use a drill and blast technique for fragmenting the rock so that it can be trucked to a crusher at the pit for further particle size reduction. The UTAC crushed material is then transported to the Fairlane Processing Plant in Forbes, MN. According to UTAC Engineers and reported in Revey, 2013, blast holes are drilled in a 23ft square pattern to depths of about 50ft. The top portion of the hole is stemmed and then up to 5000 lbs of an explosive is placed in the hole. Every blast typically involves up to hundreds of holes. Blast energy is expressed as a powder factor of the weight of the explosive divided by the weight of the blast rock. Factors have been in the range of 0.7 to 0.95 lbs per ton. 11.1 MnDOT/HDR Mine Blasting Vibration Study HDR, Inc. was retained by MnDOT to obtain seismograph readings during United Taconite blasting events that occurred within the Thunderbird Mine between the period of November, 2012 through January, 2013. The Thunderbird Mine is currently located adjacent to the existing TH 53 alignment and just to the south of the proposed E-1A alignment. An Instantel seismograph was used to record the peak particle velocity, peak particle acceleration and frequency of various blasts. HDR measured the distance between the recording location and the nearest location to the blast and obtained the charge weight per delay (lbs) from UTAC. These values were used to estimate the scaled distance for each blasting event. Scaled distance is a common parameter used in mining engineering to assess vibration magnitude from blasting on nearby structures.



HDR/Revey prepared a report (Revey, February, 2013) and presented the results of their findings to MnDOT in a September 6, 2013 workshop. In the report/workshop HDR/Revey indicated that UTAC blasting events would likely result in a maximum peak particle acceleration (PPAmax) of 0.28g in/s2. HDR also presented equations developed from the blasting monitoring data that estimate the peak particle velocity based on the scaled distance. These types of equations are often derived for different mining areas and vary based on site conditions and the type of bedrock that is being blasted. PPV = 28.83(SD)-1.178 (Equation 3) Where: PPV = Peak Particle Velocity (in/s)

SD = Scaled Distance of Blast Relative to Structure (ft/lbs1/2) The peak particle velocity can be converted into peak particle acceleration (PPA) by multiplying by 2π. 11.2 Seismic Force Parameter Input for Seismic Embankment Stability Analysis Based on the results of the HDR seismic study and workshop, we evaluated the proposed embankment using transverse peak particle accelerations (PPA) of 0.3g and 0.15g. The transverse direction is considered to be the more significant, as it represents the vibrations, and subsequent seismic forces, that would likely occur in the direction perpendicular to the centerline of the embankment. These values would need to be re-evaluated, once blasting in the vicinity is imminent. Seismic values were converted into a force for input into the embankment stability analysis by using the pseudo static method developed by Madiski and Seed (1978) and presented in FHWA SA-97-076 and 077 “Design Guidance: Geotechnical Earthquake Engineering for Highways – Vol. I & II”, 1997 and in FHWA-NHI 10-025, “Design and Construction of Mechanically Stabilized Earth Walls and Reinforced Soil Slopes Vol. II”, 2009. In this method, the calculated PPA for the transverse direction is converted into an inter-slice force for each slice in the stability analysis. This horizontal seismic force is then considered to be constantly acting on the embankment. This is why the seismic analysis is referred to as “pseudo static”, as the seismic forces are considered to be constant and acting on the embankment for a prolonged period of time. In reality, this is not the case as the seismic forces will only be acting on the embankment for a short period of time, less than a few seconds, during the blasting event. These references note that though the calculated factor of safety could fall below 1.0 momentarily, this does not mean a complete slope failure, but more likely some permanent deformation. For a seismic analysis due to an earthquake event, FHWA SA-97-076 and FHWA NHI 10-024/025 recommend reducing the seismic coefficient used in the stability analysis to ½ of the maximum acceleration value. For this analysis, we evaluated a transverse peak particle acceleration (PPA) of 0.3g as recommended by HDR, which likely represents the upper limit of seismic forces and ½ of



that value (0.15 g) as recommended by the FHWA references. Of concern would be the potential accumulation of permanent seismic deformations as a result of a number of blasting events which effect the embankment. Final design of the embankment should include the examination of this issue in more depth. Such issues that should be further evaluated include: 1) using ½ of the maximum acceleration in the pseudo-static analysis due to cumulative effects and 2) evaluating the blasting issue more realistically by performing a Quake/W dynamic finite element or similar analysis to examine the shear stress variation in the embankment. In any event, blast vibrations should be monitored as they approach the embankment and modifications made if the PPA at the embankment is higher than assumed in the final analysis. Based on the use of a granular embankment material, a minimum factor of safety of 1.1 for global stability, internal rotational and direct sliding failure modes was considered acceptable for the seismic analysis, as per guidance by FHWA –SA 97-076, 97-077 and FHWA NHI 10-024/025.

12.0 PROPOSED ROADWAY EMBANKMENT CROSS SECTION 12.1 Proposed E-1A Roadway Embankment Across Rouchleau Mine Pit The E-1A roadway profile selected contains a sag vertical curve connecting 4% and -4% grades entering and exiting the pit. Given this profile, the roadway embankment will have a maximum embankment height of approximately 170ft at approximately Station 6082+50. The roadway embankment will remain at a height ranging from 130 to 170ft above the crest of the existing submerged mine haul road embankment through the Rouchleau Pit between approximately stations 6078+00 and 6098+00 (2000ft), before decreasing in height as the roadway exits the mine pit. Figure No. 14 depicts the proposed embankment height above the existing submerged mine haul road embankment through the mine pit.



Figure No. 14: Embankment Height v. Station for E-1A Roadway Alignment

Embankment Height (ft) v. Station (100ft)

0102030405060708090100110120130140150160170180190200

6073 6078 6083 6088 6093 6098 6103

Station

Embankmnet Elevation (ft)

E‐1A Alignment Profile

12.2 Proposed Roadway Embankment Side Slope Angle The bathymetric survey identified a minimum submerged mine haul road crest width of about 500ft, between approximately stations 6089+00 and 6098+50. In order to fit the 130 – 170ft embankment on the 500ft wide mine haul road with an approximately 40ft clear zone on each side, a geosynthetic reinforced embankment will be required. We suggest a minimum 40ft clear “safety” zone from the toe of the proposed TH 53 E-1A embankment to the top crest edge of the submerged mine haul road. This 40 ft provides some tolerance 1) in case the submerged mine haul road is narrower than expected, 2) in case there is lower strength material at the edge of the submerged mine haul road and 3) to protect the roadway embankment from potential submerged haul road embankment steep slope instability during a blasting event. Based of a height of embankment as shown in Figure No. 14 and assuming a 125ft wide embankment crest with a 12ft wide bench on each side slope, the footprint width of the roadway embankment through the Rouchleau Mine Pit was determined for both 1H:1V

Design Section 1

Design Section 2

Design Section 3

Design Section 4



(45 degree) and 1H:1.7V (60 degree) embankment side slopes. Embankments composed of granular fill with side slopes of more than 35 degrees would not be stable unless the side slopes are reinforced with geosynthetics. A portion of the roadway embankment, between approximate stations 6074+00 and 6078+50 or 6081+50 can be constructed with more typical 3H:1V side slopes. This 3H:1V sideslope would not need to be reinforced with geosynthetics, and would thus allow for excavation and installation of a future bridge. This side slope recommendation is based on a submerged mine haul road to crest width in the range of 500 – 600ft wide. The following depicts our recommendation for roadway embankment side slopes through the Rouchleau Pit: - Station 6074+00 to 6081+50 (if no buried MSE wall for future bridge) 3H:1V - Station 6074+00 to 6078+50 (if buried MSE wall for future bridge) 3H:1V - Station 6081+50 or 6078+50 to 6089+00 1H:1V (45o) - Station 6089+00 to 6098+50 (narrowest portion of mine haul road) 1H:1.7V (60o) - Station 6098+50 to 6101+00 1H:1V (45o) The roadway embankment footprint width with either 1H:1V (45 degree) and 1H:1.7V (60 degree) embankment side slopes is depicted in Figure No. 15.

Figure No. 15: Estimated Embankment Footprint Width v. Station for E-1A Roadway Alignment

Embankment Footprint Width v. Station (100ft)

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

6073 6078 6083 6088 6093 6098 6103

Station (100ft Increments)

Embankment Footprint Width (ft)

E‐1A Alignment Width 1H:1V

E‐1A Alignment 1H:1.7V Sideslopes

Proposed Future Bridge Section



Geosynthetic reinforcement will be required to maintain the stability of these “steep” side slopes, especially during a blasting event. The reinforcement is installed from the face of the embankment and extending back into the embankment a length appropriate for stability. An embankment constructed with “steep” slopes on both sides, is referred to as a “back-to-back” reinforced soil slope. See Figure No. 18. The geosynthetic reinforcement for one side of the embankment should be offset vertically from the reinforcement on the opposite side of the embankment so that there is at least 6 inches to 1 ft vertical separation between all geosynthetic layers. Tall geosynthetic reinforced slopes have been built throughout North America, Europe and Asia over the past 30 years. Gale-Tec Engineering, Inc. including Stephan Gale, PE, D. GE, F.ASCE and Dr. Barry Christopher, PhD, PE, D. GE – both experienced in Geosynthetic Reinforced Soil Structures (RSS), presented a workshop to MnDOT in November, 2013. Tall geosynthetic reinforced slopes have been designed and built using the present design technology. Projects include: 242 ft high RSS at Yeager airport in Charleston, WV, 200 ft high RSS at Crystal Cove in Newport Beach, CA, and a 100 ft high RSS on Meigs County CSAH 124 for Ohio DOT. Other local projects include: RSS along CSAH 42 at Mississippi River for Wright County, RSS along TH 100 at Breck School for MnDOT and CSAH 20 in Cannon Falls, MN. The CSAH 42 project was reinforced below the high water level. The back to back condition, as well as the height (up to 170 ft) of the embankment and the seismic consideration excludes this RSS embankment from being designed using the standard MnDOT RSS template, Standard Sheet No. 5-297.646 to 649. Once final parameters are selected, the embankment geometry will have to be re-analyzed/designed without regard for the MnDOT design template.

12.3 Design Cross Sections

Four (4) design embankment cross sections were selected from the roadway alignment profile to analyze for stability and settlement. The design sections include a proposed roadway embankment crest width of 125 ft. We analyzed 1H:1V (45 degree) geosynthetic reinforced side slopes at Stations 6082+50, and 1H:1.7V (60 degree) sides slopes at Stations 6090+50 and 6095+00. At Station 6090+50, we analyzed a 12ft wide midslope bench. Between Stations 6073+50 and 6078+50, a future bridge will be installed. At this location we analyzed 3H:1V un-reinforced side slopes. The mine waste rock fill surface elevation and thickness used in the analysis were from the 2013 MnDOT bathymetric survey, the 2013 MnDOT marine resistivity survey and the rock borings. The cross section details are described in the following paragraphs. Design Section 1: Section No. 1 was chosen at Station 6077+00, where the embankment height is approximately 100ft. This cross section occurs where the proposed roadway alignment has just entered the pit from the south east and where the ground surface for the proposed TH 53 roadway embankment is not currently submerged. A proposed bridge will be constructed at this station in the future. 3H:1V embankment sideslopes, which do not require geosynthetic reinforcement, are proposed at this location so future excavation



for the bridge foundations can be performed without cutting into or removing geosynthetic reinforcement. Boring 31073 was performed near this station. This boring shows that mine waste rock fill is present from the ground surface at elevation 1305 ft, to a depth of approximately 70 ft, or an elevation of approximately 1235 ft. Cherty bedrock was encountered at elevation 1235 ft. Design Section 2: Section No. 2 is where the roadway embankment is at its’ maximum height of 170 ft at approximately Station 6082+50. Borings 31086 and 31072 were performed nearest to this station. These borings show that the mine waste rock fill surface is at an elevation of approximately 1284-1290 ft and that the mine waste rock fill/bedrock interface is at an elevation of approximately 1270 ft on the south side of the submerged haul road embankment and 1200 ft on the north side of the submerged haul road embankment. This cross section is located in the south east portion of the mine pit in an area where the 500 ft wide submerged haul road embankment transitions into a wider area of mine waste rock fill placement. Design Section 3: Section No. 3 was chosen at Station 6090+50. At this location, the roadway embankment height is approximately 150 ft, and is located adjacent to a submerged haul road embankment 80ft high sideslope slope at 1.3H:1V (38 degrees) on both the north and south sides of the roadway embankment. The embankment footprint width at this section is approximately 300 ft assuming 60 degree side slopes and approximately 400 ft assuming 45 degree side slopes. A 12 ft bench was added to the midpoint of embankment side slopes at elevation 1370ft. Boring 31070 was performed nearest to this station. This boring shows that the submerged haul road embankment crest is at an elevation of approximately 1280 ft and that the mine waste rock/bedrock interface is at an elevation of approximately 1240 ft beneath the proposed roadway embankment. Design Section 4: Section No. 4 was chosen at Station 6095+00. At this location, the roadway embankment height is approximately 135 ft, and the submerged haul road embankment is at its’ narrowest width of approximately 500 ft. The embankment footprint width at this section is approximately 300 ft assuming 60 degree side slopes and approximately 400ft assuming 45 degree side slopes. The submerged haul road embankment has 80 – 100ft high side slopes that extend down into the pit on both sides of the embankment at approximately 1.3H:1V (38 degree) slope angles. Borings 31069 and 31082 were performed nearest to this station. These borings show that the submerged haul road embankment crest elevation is approximately 1284 -1290 ft and that the mine waste rock/bedrock interface is at an elevation of approximately 1200 ft on the south side of the submerged haul road embankment and 1170 ft on the north side of the submerged haul road embankment. 12.4 Potential Mine Waste Rock Fill/Bedrock Weakened Interface Based on the results of the resistivity survey, it was postulated that the potential for a weakened or sloping interface exists between the mine waste rock fill material and the bedrock within the submerged haul road embankment, though this resistivity difference may also be waste rock fill that was placed at difference times with different properties.



The resistivity survey indicated that the bedrock elevation within the embankment is likely variable both in elevation and dip orientation. This weakened layer at the mine waste rock fill/bedrock interface may have resulted from the migration of the finer (sand sized) mine waste rock fill particle down through the submerged mine waste rock fill embankment to the bedrock interface. The void space present within the mine waste rock fill is large enough for this migration of sand sized particles to have occurred. To investigate if this potential weakened interface could govern the stability of the proposed TH 53 roadway embankment, a seismic slope stability analysis was performed at station 6095+00. For this analysis, the angle of internal friction of the weakened interface was estimated at 35 degrees, a value that is typical for a sand material under relatively high confining stresses. This value was also chosen relative to the value of the mine waste rock fill (41.5 degrees), as it was estimated that the potential weakened interface would consist of migrated finer particles from this material. The orientation of the potential weakened interfaced was varied within the submerged haul road embankment to determine if a particular orientation and elevation would result in a lowered factor of safety. The orientation of the weakened interfaced was varied between horizontal and inclined at approximately 1.3H:1V slope angle, the same as the submerged haul road embankment sideslopes. The end of the horizontal portion of the weakened interface relative to the submerged haul road embankment slope face was also varied. The elevation of the horizontal weakened interface was varied approximately between 1200ft and 1240ft, which is approximately equal to the bedrock elevations within the submerged haul road embankment within this area. This analysis considered the seismic stability, as the static stability had higher factors of safety. A transverse PPA of 0.3g, the maximum peak particle acceleration recommended by HDR, 2013, was used. The vertical PPA component was assumed to be zero, as it was in the other analyses. The results of this analysis are presented in Section 14.5. 13.0 PROPOSED ROADWAY EMBANKMENT CONSTRUCTION METHODS The proposed TH 53 embankment across the Rouchleau Pit will be over a submerged mine haul road embankment. The existing embankment is submerged under about 30 ft of water based on an August, 2013 water level measurement and the 2013 MnDOT bathymetric survey. The Bathymetric survey indicated that the crest of the submerged haul road embankment is at an elevation ranging from 1285ft – 1280ft. 13.1 Removal of Vegetation/Debris, Trees and Organic Soils on Submerged Haul Road Embankment Crest prior to Embankment Construction Aerial photos taken in the late 1990’s and early 2000’s indicate that trees and other woody vegetation are present on the crest of the submerged haul road embankment. The tops of some of these trees are still visible today. It is estimated that the trees present on



the embankment have trunk diameters ranging from 6 -12 inches. These trees will need to be removed from the submerged haul road embankment crest prior to roadway embankment construction. If the Rouchleau Mine Pit water elevation is lowered to 1274 ft or lower, then the trees and other vegetation can be removed using conventional clearing and grubbing methods. If the embankment is to be constructed in wet conditions, a dredging operation will likely be required. The presence of vegetation on the submerged haul road embankment crest indicates the potential for an organic/topsoil layer to be present as well. Core samples and observations during drilling did not turn up evidence of a topsoil layer present on the submerged haul road embankment crest. A MDNR Mine Reclamation Statute from 1980, and still enforced today, required that 2 ft of soil cover be placed over all mine stockpiles at the time of mine closure, though there are no records of cover soil being placed. Regardless, it is recommended that any organic or other deleterious material be removed from beneath the footprint of the proposed roadway embankment prior to construction. The presence of this layer could be further investigated once pit dewatering has been completed. If the final construction plan is not to dewater the pit, the lower portion of the embankment would be constructed in the wet. If this were to occur, we recommend that probes be performed from a barge, using divers or remotely operated equipment mounted with a camera (e.g. Shaft Inspection Device – SID) to investigate the presence of a topsoil layer and surface debris. If present, the removal of topsoil, debris and trees by dragline could be implemented. Inclusion of a “topsoil” layer at the base of the proposed roadway embankment could result in a “weak” or potential shear zone at the base of the embankment. 13.2 Embankment Construction in Dry Conditions by Lowering the Water in the Entire 2 Miles Long Series of Mine Pits including the Rouchleau Pit In order to construct the proposed TH 53 E-1A embankment across the Rouchleau Pit in the dry, lowering of the water level in the series of mine pits east of the City of Viginia will be required. We recommend the pit water level be lowered to a depth of approximately 6 ft below the submerged haul road embankment crest surface, or to an approximate elevation of 1274 ft based on ground improvement considerations. (See Report Section 19.0). The water level in the pit will need to remain at an elevation of approximately 1274 ft during ground improvement and for the initial portion of embankment construction. Once embankment construction has achieved an elevation of approximately 1310 – 1320 ft, or approximately 30 – 40 ft above the existing mine waste rock fill surface, then the dewatering can be terminated and the Rouchleau Pit water level allowed to rise back up to its’ pre-dewatered level.



If the entire Missabe Mountain Pit Lake was drawn down, a source for the pumped water would be required. A study by HDR Engineering, Inc. and Gale-Tec Engineering, Inc. (HDR, 2014) estimates an initial time period of 3 months to draw the Rouchleau Pit water level down 30 ft if pumping levels are maintained at 25,850 gpm. This relatively high predicted pumping rate is a result of our assumption that time will be of the essence – and it will take time to not only pump but to order and install the pipe lines and pumps/motors. If the time (3 months) allotted for pumping can be increased to approximately 12 months, then the rate could be reduced to approximately 6000 – 8000 gpm. Maintenance pumping at a rate of 5400 gpm is estimated to maintain the Missabe Mountain Pit Lake (Rouchleau Pit) at this 30 ft drawdown level (HDR, 2014). 13.3 Embankment Construction in Dry Conditions with Levee-Geotextile Tube Cofferdam Constructed in Wet Conditions and then Construction Zone Dewatering Construction of the embankment in dry conditions could occur one of two ways without drawing the water level down in the entire Rouchleau Pit; 1) a cut-off system consisting of soil/rock levees or a stacked geotextile tube system could be installed on both sides of the crest of the submerged haul road embankment and an upstream blanket placed, then dewatering could occur within the footprint of where the proposed highway embankment is to be constructed and 2) a cut-off levee or stacked geotextile tube system could be installed on only the north side of the submerged haul road and an upstream blanket placed and only the south portion of the Rouchleau Pit dewatered. The cut-off levee or geotextile tube system would likely require an upstream blanket be placed to reduce underseepage. A sodium bentonite mat needle stitched to a woven/nonwoven fabric (Geosynthetic Clay Liner or GCL) with an attached 20 mil HDPE geomembrane or a geomembrane alone could be deployed on the water side of the levee and then extended upstream a certain distance to act as an upstream blanket so as to reduce underseepage when dewatering the construction zone. The GCL mats are typically manufactured in 15 ft wide by up to 200ft long. The mat could be covered with a gravel or attached to a Reno-Mattress system for ballast. This system would need to be further investigated. The common sheet pile cofferdam method would have difficulty penetrating into the mine rock fill and would likely not be a reliable water cut-off. With this approach the crushed rock/granular fill levee could be placed into the standing water by the “plunging the Dozer” method, which consists of pushing fill into standing water and displacing any topsoil or soft soils that may be present. Similar techniques have been used for construction of the Mora, MN airport runway and for the nearby United Taconite Tailings Dike No. 1 (Gale, et. al., 1983). The United Taconite Tailing dike is a 200 ft high structure.



Depending on the final width of the embankment, this levee/geotextile tube system may not have to be a part of the structural embankment; and thus the risk of some distortion occurring may be able to be tolerated. Geotubes®, as termed by one manufacturer, are large diameter high strength woven geotextile tubes which could be deployed under water and then filled with a sand slurry. The tubes would be filled from a slurry box with import sand or fine tailings potentially excavated from one of the nearby Mining Companies tailing basins. Based on previous projects, each tube could be 51 ft in circumference and each tube pumped to about 9 ft high. A 3 to 4 layer stack would be required to achieve a 25 ft height. Geotextile tubes have been used in marine environments on projects throughout the world since the 1980’s. The Incheon Bridge project in Korea (Geosynthetics, 2014) demonstrates using Geotubes® to construct an outer perimeter containment structure. The construction platform for construction of bridge foundations was created inside the perimeter of the tubes for this project. A magazine article on this project is attached in the Appendix. Once the perimeter levee/geotube system was up, pumping could begin. A simplified seepage analysis, indicates that if the levee is composed of sand fill, which is two orders of magnitude less permeable than the in-place mine waste rock fill, then 97% of the seepage into the construction zone would be underseepage coming up from the mine rock fill. The mine waste rock fill permeability is unknown and was estimated for this simplified analysis. Slug/pump tests are planned for Spring 2014 to further refine the mine waste rock fill permeability. Based on a simplified analysis of construction zone dewatering without an upstream blanket, a preliminary estimate of the volume of water from dewatering would be approximately 135 million gallons for initial drawdown and 10,000 – 50,000 gallons per minute depending on the permeability of the buried mine waste rock fill and the upstream blanket method for reducing underseepage. As a result of this high water volume prediction, we recommend that an upstream blanket be considered for this case. If a levee or stacked geotextile tube cofferdam system was used, the pumped water could be returned to the Missabe Mountain Pit Lake. 13.4 Embankment Construction (Lower 30 ft) in Wet Conditions with Embankment Fill Placement Into Standing Water The lower 30 ft of the embankment could be constructed into standing water – maintaining a 40 ft “safety zone” from the edge of submerged mine haul road embankment and the proposed reinforced embankment toe. After removal of trees and debris by backhoe or dragline, a “plunging the dozer” technique as described in Section 13.3, could be used with a crushed rock material that would likely need to be processed before placing. With this approach, there is a risk that soft or compressible soil may not be displaced which could result in embankment instability. Additionally, the friction angle of the uncompacted material may be low, resulting in a shallow slope requirement under the effects of a blast. If this approach is considered, further friction angle testing



of the underwater fill is recommended. One of the disadvantages of this approach would be that geosynthetic reinforcement of the lower 30 ft of the embankment could NOT be installed – resulting in more reinforcement above the water level to maintain stability as a result of the seismic embankment analysis. 13.5 Utilities within Proposed Embankment The TH 53 Relocation Draft EIS (Kimley-Horn, 2014) notes that there are two public and four private utility operators located within an existing easement within the TH 53 right-of-way. These utilities include storm sewer, sanitary sewer (18 inch pipe), water main (10 inch pipe), gas (3 inch low pressure pipe), overhead electrical, Century Link (9 – 4 inch PVC conduits) and two fiber optic cables. Utilities will likely be replaced in the new TH 53 embankment beneath the Mesabi Trail portion of the embankment crest. Once the geosynthetic reinforcement has been placed and the embankment has been constructed, excavation for utility installation will not be possible without increasing the risk of embankment instability. There would also be a risk of instability if the geosynthetic was cut to get access to and maintain the utilities. A leaking water main, storm or sanitary pipe can be a potential source for water seeping into the reinforced or unreinforced embankment fill which could result in saturated soil conditions, erosion within the reinforced embankment fill and potential instability. Instability is exasperated as a result of the proposed steep embankment side slopes. Recommendations for utility installation within the proposed embankment that mitigate the above referenced risks are given in Section 26.0. 14.0 ANALYSIS –PROPOSED TH 53 E-1A ROADWAY EMBANKMENT ACROSS ROUCHLEAU PIT 14.1 Settlement Analysis of Proposed Embankment A settlement analysis was performed at the four (4) design cross sections; Stations 6077+00, 6082+50, 6090+50 and 6095+00. The settlement analysis involved determining the effective stress increase in the mine waste rock fill foundation material due to the construction of the proposed embankment and then estimating the compression of the mine waste rock fill and the embankment fill material. The intact bedrock beneath the mine waste rock fill was assumed to be incompressible relative to the mine waste rock fill and the embankment fill material. The compression of the mine waste rock fill was assumed to behave as a linear elastic material, meaning that the deformation that occurs due to the increase in stress will be directly proportional to the static modulus of the mine waste rock fill. This analysis was performed assuming that no ground improvement measures (such as Dynamic Compaction) were performed. As such, the static modulus of the upper portion of mine waste rock fill was not increased relative to the lower portions of the submerged haul road embankment. Since our assumption was a linearly elastic material, a drawdown of the water in the pit at the time of mining should not result in additional settlement. We



expect most of the settlement should occur during construction, although some post construction settlement could occur due to blasting nearby.

14.1.1 Effective Stress Increase due to Embankment Construction The vertical effective stress increase in the foundation (mine waste rock fill) material along the proposed embankment alignment was determined using the Boussinesq stress distribution method for embankments summarized in Das (2006) and given in Equation 4.

( ) ⎥⎦

⎤⎢⎣

⎡−+⎟⎟

⎠

⎞⎜⎜⎝

⎛ +=Δ 2

2

121

2

21 αααπγσ

BB

BBBH Equation 4

Where: γ = Density of embankment soil (pcf) H = embankment height at centerline (ft) B1 = width of embankment crest from top of slope to point of interest (ft) B2 = length of embankment side slope (ft)

⎟⎠⎞

⎜⎝⎛−⎟

⎠⎞

⎜⎝⎛ +

=zBa

zBBa 121

1 tantanα (radians)

⎟⎠⎞

⎜⎝⎛=

zBa 1

2 tanα (radians)

z = depth of interest (ft) To estimate the stress increase in the mine waste rock fill layer (beneath the embankment crest centerline), the foundation material was separated into 1ft vertical increments using a Microsoft Excel spreadsheet. The stress increase at each increment was then calculated. The stress increase was calculated at each cross section assuming mine waste rock fill layer thicknesses ranging between 30 ft and 110 ft. The stress increase calculated for the bottom and for the top of the mine waste rock fill for the various embankment heights is included in Table No. 4. A sample calculation is included in the Appendix.

Table No. 4: Stress Increase (Δσ) in Mine Waste Rock Fill beneath Centerline of

Proposed Embankment

Stress Increase for 170ft Embankment




Mine Waste

Rock Fill Thickness

(ft) Bottom* Top* Bottom* Top* Bottom* Top* Bottom* Top*

30ft 19,600 psf

21,200 psf 17,200 psf

18,700 psf 15,400 psf

16,800 psf 10,900 psf 12,500 psf

50ft 18,500 psf

21,200 psf 16,100 psf

18,700 psf 14,400 psf

16,800 psf 9,900 psf 12,500 psf

70ft 17,500 psf

21,200 psf 15,150 psf

18,700 psf 13,400 psf

16,800 psf 9,000 psf 12,500 psf

90ft 16,500 psf

21,200 psf 14,200 psf

18,700 psf 12,500 psf

16,800 psf 8,200 psf 12,500 psf



110ft 15,500 psf

21,200 psf 13,300 psf

18,700 psf 11,700 psf

16,800 psf 7,500 psf 12,500 psf

*Bottom = Bottom of Mine Waste Rock Fill Layer, *Top = Top of Mine Waste Rock Fill Layer 14.1.2 Mine Waste Rock Settlement Parameters As previously indicated, the compression of the mine waste rock fill is assumed to behave as a linear elastic material, meaning that the deformation that occurs due to the increase in stress would be directly proportional to the static modulus (Es) and Poisson’s ratio (μ ) of the mine waste rock fill. In the linear elastic model, the amount of strain, or settlement, induced in the material layer is calculated using Equation 4 (Duncan et al, 1980).

( )( )( )μ

μμσε−

−+Δ=

1211

sE Equation 5

Where: ε = strain or settlement of the material layer σΔ = induced stress caused by embankment construction (from Equation 4) Es = static modulus of the material layer μ = Poisson’s ratio of the material layer The static modulus of the mine waste rock fill was discussed in Section 8.4. For this analysis, values ranging from 300,000 to 550,000 psf were assumed for the static modulus of the mine waste rock fill. A Poisson’s ratio of 0.33 was assumed for the mine waste rock fill material. According to the boring results, the mine waste rock fill depth varies from approximately 30ft to 120ft beneath the proposed embankment. The results of the resistivity indicate that the mine waste rock/bedrock interface may also vary significantly in height through the submerged haul road embankment cross section. Due to this variability, the settlement analysis was performed assuming mine waste rock fill thicknesses of 30ft, 50ft, 70ft and 90ft. 14.1.3 Geosynthetic Reinforced Embankment Fill Settlement Parameters The compression of the compacted reinforced embankment fill was estimated from the empirical correlation in NAVFAC DM-7.2, Foundations and Earth Structures, (1982). A compression value of 1% of the height was used. This embankment fill compression was added to the mine waste rock fill compression to estimate total settlement. 14.1.4 Settlement Analysis: Design Station 1 - Station 6077+00, 100ft Embankment Height The settlement analysis was performed at station 6077+00, assuming a 100ft high granular embankment. The mine waste rock thickness near this station is approximately



70 ft based on the results of one boring, but is likely to vary as estimated in Table No. 5. The amount of settlement was calculated beneath the centerline of the embankment. A range of settlement values was determined based on the likely variability in the static modulus of the mine waste rock fill material. Settlement of the embankment itself was also included in the analysis. The results of the settlement analysis for this design station are given in Table No. 5.

Table No. 5: Calculated Range of Embankment Settlement for Station 6077+00 (100ft Embankment Height)

Mine Waste Rock

Layer Thickness (ft) Estimated Settlement of

Reinforced Fill Embankment (ft)

Estimated Range of Settlement for Mine Waste Rock Fill (ft)

Estimated Total Settlement (ft)

50ft 1.0ft 0.7 – 1.3ft 1.7 – 2.3ft 60ft 1.0ft 0.8 – 2.2ft 1.8 – 2.5ft 70ft 1.0ft 0.9 – 1.7ft 1.9 – 2.7ft 80ft 1.0ft 1.0 – 1.9ft 2.0 – 2.9ft 90ft 1.0ft 1.1 – 2.0ft 2.1 – 3.0ft

Based on Table No. 5, total settlement could be in the range of 2 – 3 ft, with differential settlement across the cross section in the range of ½ to 1 ft. Much of this settlement will likely occur during construction and/or within 2 – 4 months after embankment completion. Monitoring will be important during construction. 14.1.5 Settlement Analysis: Design Station 2, Station 6082+50: 170ft Embankment Height The settlement analysis was performed at station 6082+50 assuming a 170 ft high reinforced granular embankment. The mine waste rock thickness near this station could vary from 20 to 90 ft, south to north across the cross section. The amount of settlement was calculated beneath the centerline of the embankment. A range of settlement values is reported considering the likely variability in the static modulus of the mine waste rock fill material. Settlement of the granular embankment was added to the settlement of the mine waste rock fill to get the total settlement. The results of the settlement analysis for this design station are given in Table No. 6.



Table No. 6: Calculated Range of Embankment Settlement for Station 6082+50 (170 ft

Embankment Height)

Mine Waste Rock Layer Thickness (ft)

Estimated Settlement of Reinforced Granular Fill

Embankment (ft)



20 ft 1.7ft 0.4 – 1.0ft 2.0 - 2.7ft 40 ft 1.7ft 1.0 – 1.7ft 2.7 - 3.5ft 60ft 1.7ft 1.4 – 2.4ft 3.1 – 4.3 ft

80ft 1.7ft 1.9 – 3.4ft 3.6 – 5.1 ft Based on the results of the borings and marine resistivity survey, it is likely that the mine waste rock fill thickness can vary from 20 to 90 ft thick from south to north at Station 6082+50. Total settlement is estimated to be in the range of 2 – 5 ft; with differential settlement across the cross section in the range of 2 – 3 ft. Much of this total and differential settlement will likely occur during construction and/or within 2 – 4 months after embankment completion. Monitoring during construction will be important. 14.1.6 Settlement Analysis: Design Station 3, Station 6090+50: 150ft Embankment Height The settlement analysis was performed at station 6090+50, assuming a 150 ft reinforced granular fill embankment. The one boring performed at this cross section and the marine resistivity survey indicate the mine waste rock thickness to be relatively uniform across the cross section with a thickness of 40 ft. A range of settlement values was determined based on the likely variability in the static modulus of the mine waste rock fill material and potential variation in the mine waste rock fill thickness across the cross section. Settlement of the granular embankment was included in the analysis. The results of the settlement analysis for this design station are given in Table No. 7.

Table No. 7: Calculated Range of Embankment Settlement for Station 6090+50

(150 ft Embankment Height)

Mine Waste Rock Layer Thickness (ft)

Estimated Settlement of Reinforced Granular Fill

Embankment (ft)



20ft 1.5ft 2.0 – 2.3ft 3.5 – 3.8ft 30ft 1.5ft 2.1 – 2.7ft 3.6 – 4.2ft



40ft 1.5ft 2.4 – 3.1ft 3.9 – 4.6ft 50ft 1.5ft 2.6 – 3.5ft 4.1 – 5.0ft 60ft 1.5ft 2.8 – 3.8ft 4.3 – 5.3ft

Total settlement is estimated to be in the range of 2½ - 5½ ft with differential settlement across the cross section of ½ - 2 ft. Much of this total settlement and differential settlement, if it occurs, will likely occur during construction and/or within 2 – 4 months after embankment completion. Monitoring during construction will be important. 14.1.7 Settlement Analysis: Design Station 4, Station 6095+00: 135ft Embankment Height The settlement analysis was performed at station 6095+00 assuming a 135ft high reinforced granular fill embankment. Based on the results of the boring and electrical resistivity survey performed in this area, it is likely that the mine waste rock fill thickness can vary from 90 ft to 120 ft thick, south to north at Station 6095+00. A range of settlement values is reported considering the likely variability in the static modulus of the mine waste rock fill material. settlement of the reinforced granular embankment was added to the mine waste rock fill to get the total settlement. The results of the settlement analysis for this design station are given in Table No. 8.

Table No. 8: Calculated Range of Embankment Settlement for Station 6095+00 (135ft Embankment Height)

Mine Waste Rock Layer

Thickness (ft) Estimated Settlement of Reinforced Granular Fill

Embankment (ft)


Estimated Total

Settlement (ft)

90ft 1.3ft 1.7 - 3 ft 3.0 - 4.3 100ft 1.3ft 1.2 – 2.1ft 2.5 – 3.4 110ft 1.3ft 1.4 – 2.3ft 2.7 – 3.7 120ft 1.3ft 1.5 – 2.7ft 2.8 – 4.0

*Mine waste rock fill varies from 90 ft thick on south side to 120 ft thick on north side. Total settlement is estimated to be in the range of 2 – 4ft with differential settlement across the cross section of 1 – 2ft. Much of this total and differential settlement will likely occur during construction and/or within 2-4 months after embankment completion. Monitoring during construction will be important. 14.2 Stability Analysis of Proposed Roadway Embankment An embankment stability analysis was performed at the four (4) design cross sections: Design Station 1 Station 6077+00 – 100 ft embankment height, Design Station 2 Station



6082+50 -170ft embankment height, Design Station 3 Station 6090+50 - 150ft embankment height and Design Station 4 Station 6095+00 - 135ft embankment height. The analysis at each cross section included a static analysis and a seismic analysis. Both these analyses were performed using a limit equilibrium method. In this method, a factor of safety against embankment instability is calculated based on the shear strength of the embankment fill and the foundation mine waste rock fill. The analyses were performed using the computer program Slope-W by Geostudios, Inc. and ReSSA 2.0 by Adama Engineering, Inc. In addition, a Monte Carlo probability analysis was performed as part of Slope-W to assess the variability in the factor of safety in terms of the uncertainty of the strength input parameters and a numerical FLAC-Slope analysis was performed to assess zones of potential deformation. 14.2.1 Static and Seismic Analysis Static and seismic stability analyses were performed in substantial accordance with FHWA-NHI-10-025 (Nov. 2009). The Spencer method of limit equilibrium analysis was used for the Slope-W analysis. The AASHTO-Bishop method of limit equilibrium analysis was used for the ReSSA analysis. The methods analyze potential circular or wedge shear surfaces by separating the soil above the proposed failure plane into multiple segments and then uses both force and moment or moment equilibrium to balance the forces in each segment. In the case of the seismic analysis, a pseudo-static seismic force is induced on the embankment to simulate a blasting event. The ReSSA computer program was used to evaluate internal circular failure surfaces internal to the RSS that results in a failure of the geosynthetic reinforcement and direct sliding failure surfaces both internal to the RSS reinforcement layers and about the RSS base. The Slope-W computer program was used to evaluate global or compound failure surfaces that involved both the proposed RSS embankment and the in-place submerged haul road embankment. Both programs have a search process in which minimum factors of safety are searched for by an iteration process. Table No. 9 includes suggested minimum factors of safety per Berg, Christopher and Samtani (FHWA-NHI-10-025, Nov. 2009).



Table No. 9: Minimum Factors of Safety

Failure Mode

Minimum Static Factor of Safety

Minimum Seismic Factor of Safety

Direct Sliding 1.3

1.1

Compound (Global) Stability

1.3 1.1

Internal Rotational

1.3

1.1

14.2.2 Monte Carlo Probability Analysis Monte Carlo probability analyses were performed as part of the seismic analysis at Stations 6082+50, 6090+50 and 6095+00 to assess how the uncertainty in the in-place mine waste rock and the proposed reinforced embankment fill strength parameters affect the global stability and direct sliding factors of safety. In a Monte Carlo slope stability analysis, an input parameter that contains uncertainty is quantified by assuming a Gaussian normal distribution with a mean and a standard deviation. For this analysis, the angle of internal friction of the mine waste rock fill and the angle of internal friction of the reinforced embankment fill were selected. The computer selects a random friction angle value based on a normal distribution, and calculates the embankment factor of safety based on that number using conventional limit equilibrium techniques. After 2000 random friction angle values are selected and factors of safety calculated, the computer takes all of the calcuated factor of safety values and generates a normal distribution with respect to the factor of safety. From this, a factor of safety is associated with a probabilty of failure. The Monte Carlo analysis uses five standard deviations to calculate a minimum and maximum value, which equates to about 1 in 1000 (99.9%) of a sample size. The input parameters for the Monte Carlo simulations performed at Stations 6082+50 and 6095+00 are given in Table No. 10. A typical factor of safety output in the form of a normal distribution is given in Figure No. 16. The results of the Monte Carlo simulations are given in Sections 14.3.4.



Table No. 10: Monte Carlo Statistical Analysis Input Parameters

Parameter Mean (deg)

Standard Dev. (deg)

Min. Value* (deg)

Max. Value * (deg)

Mine Waste Rock

Friction Angle 43 4 23 63

Reinforced Embankment Fill Friction

Angle

35

2

25

45

*Minimum and Maximum values are calculated based on five (5) Standard Deviations from the Mean Figure No. 16: Results of Monte Carlo Probability Analysis: Factor of Safety Distribution

Probability Density Function

Freq

uenc

y (%

)

Factor of Safety

0

5

10

15

20

1.023 1.083 1.143 1.203 1.263 1.323 1.383 1.443 1.503 1.563

14.2.3 Finite Element Embankment Stability Modeling to Identify Shear Displacement Zones Fast Lagrangian Analysis of Continua (FLAC) is a general purpose program for numerical modeling of continuous materials. FLAC-Slope, a version of FLAC, provides an alternative to traditional limit equilibrium programs for determining the factor of safety against embankment instability. Limit equilibrium codes use an approximate scheme in which a number of assumptions are made, i.e. for example, the location and angle of interslice forces. For the Slope-W and ReSSa analyses, the computer generates failure surfaces with the lowest factor of safety is identified. FLAC-Slope provides a solution of the coupled stress/displacement, equilibrium and constitutive equations by using finite elements. The factor of safety is found to correspond to the point of stability and the critical failure surface is identified. The advantage of FLAC-Slope is that it generates zones of shear distortion. FLAC-Slope analyses were performed as part of the seismic stability analysis at design stations 6082+50 and 6095+00. The analyses were performed to corroborate the factors of safety and failure plane locations calculated by limit equilibrium methods and also to



identify potential zones of deformation which can then be used as guidance for the placement of instrumentation in the field. The FLAC model was not calibrated for strain magnitude; in order to predict the magnitude of strain, the modulus and poisson’s ratio for the selected embankment fill and the selected reinforcement geosynthetic would need to be further assessed. A typical FLAC-Slope model output is given in Figure No. 17. The results of the FLAC-Slope modeling are given in Sections 14.3.5.

Figure No. 17: FLAC-Slope Modeling with Respect to Embankment Factor of Safety

14.2.4 Proposed Roadway Embankment Typical Section The embankment section considered in the stability analysis consisted of a granular embankment fill which was assumed to have an in-situ unit weight of 125 pounds per cubic foot. Embankment side slopes of 1H:1V (45 degree), 1H:1.7V (60 degree) and 3H:1V were analyzed. A 125 ft wide roadway embankment crest was assumed, which will create a back-to-back RSS embankment condition, meaning that the geosynthetic reinforcement from one side slope would have to be placed at a vertical offset from the geosynthetic reinforcement from the opposite side slope, so as to avoid intersection in the interior portion of the embankment. A typical back-to-back 1H:1.7V embankment section is illustrated in Figure No. 18. A midslope 12ft wide bench was also considered. A riprap material was considered at the slope face where the slope may be below the long-term Rouchleau Pit water level.



The required geosynthetic embedment length, vertical offset and geosynthetic strength properties were evaluated for each design cross section. Figure No. 18: Typical 1H:1.7V Side Slope RSS Embankment Section used in Stability

Analysis

14.2.5 Mine Waste Rock Strength Parameters for Analysis Based on the literature review and the mine waste rock friction angle variation evaluation, the mine waste rock fill shear strength models were developed for both the material beneath the proposed highway embankment that will experience an increase in effective stress, and the material outside of the footprint of the proposed embankment that will not experience an effective stress increase due to embankment construction. For this analysis, the mine waste rock fill beneath the proposed roadway embankment was assumed to have a friction angle varying from 43.5 degrees near the top of the submerged mine haul road embankment (approximately elevation 1280ft) to 41.9 degrees at the base of the submerged mine haul road embankment (approximately elevation 1200ft). The friction angle was reduced by a value of 0.2 degrees for every 10ft in depth.



For this analysis, the mine waste rock fill, outside the footprint of the proposed roadway embankment, was assumed to have a friction angle that varied from 60 degrees near the top of the submerged mine haul road embankment (approximately elevation 1280ft) to 44 degrees at the base of the submerged mine haul road embankment (approximately elevation 1200ft). For this analysis, the density of the mine waste rock was estimated to be 180 pcf. This density was approximated by assuming a specific gravity of 4.1 for the Cherty and Slaty rock material from the Biwabik Iron Formation and a mine waste rock fill porosity of approximately 25%. 14.2.6 Granular Embankment Fill Material Gradation, Unit Weight and Strength Parameters for Analysis For this analysis, it was assumed that the proposed roadway embankment would be constructed with a granular material with a maximum particle size in the range of 3 to 4 inches diameter and a per cent passing the US No. 200 sieve of 12% by dry weight. The embankment fill material was assumed to have a in-situ unit weight of 125 pcf and an angle of internal friction per ASTM D3080 (Direct Shear Testing) of 35 degrees at 95% of the maximum T-99 Proctor dry density. These values are reasonable assumptions for a screened glacial till type soil – but not a crushed mine rock material. This type of material would have a much higher unit weight and a higher angle of internal friction. As such, the stability analysis would need to be re-evaluated if a crushed mine rock fill was used for the reinforced embankment. It was assumed that aggregate (riprap) material would be placed on the embankment side slopes below the long term Rouchleau Pit water level. This aggregate would consist of a material similar to the mine waste rock fill present along the proposed roadway alignment. Therefore, the density and angle of internal friction of the rock fill used on the embankment side slopes were assumed to be the same as the mine waste rock material, a density of 180 pcf and an angle of friction of 50 degrees. 14.2.7 Geosynthetic Reinforcement Properties for Analysis Geosynthetic reinforcement is required to maintain stability of the proposed 1H:1V (45 degree) or 1H:1.7V (60 degree) embankment side slopes. The Design Long Term Reinforcement Nominal Tensile Strength (Tal) of the uniaxial geosynthetic material was determined by taking the Ultimate Strength in the machine roll direction by ASTM D-6637 (for geogrids) or ASTM D-4595 (for geotextiles) and reducing that strength to account for creep, installation damage and durability per FHWA-NHI-10-024/025. An interaction coefficient between the geosynthetic and the embankment fill of approximately 85% of the embankment fill friction angle was assumed. The horizontal geosynthetic length and vertical offset between adjacent layers were evaluated within the SlopeW and ReSSA stability analyses. Geosynthetic reinforcement material recommendations are given in Section 22.0.



14.2.8 Rouchleau Mine Pit Water Elevation used for Analysis The stability analysis at the design cross sections was performed using several different static water levels and a water level that varies across the embankment as would occur if a mining company dewatered the southern portion of the Rouchleau Pit some time into the future. Static water levels of 1280ft and 1320ft were assumed for each of the four (4) design cross sections. A water level of 1280ft would likely result just after construction if dewatering were performed. A static water level of 1320ft was assumed during the course of the embankment design life; though a higher level could result. This “high” water level needs to be further evaluated for final design. We assumed that a mining company will, at some point in the future, dewater the southern portion of the Rouchleau mine pit to an elevation of the existing bedrock (approximately elevation 1200 to 1240 ft) in order to mine taconite ore from the area. This dewatering will likely temporarily induce short term seepage pressures in both the existing submerged haul road embankment and the proposed geosynthetic reinforced granular embankment. Seep-W, from the suite of Geostudios, Inc. programs, was used since it is interactive with Slope-W. This finite element program evaluates the line of seepage, seepage pressures and flow rates. A simplified seepage analysis was performed for design stations 6082+50 (Seepage Run No. 1), 6095+00 (Seepage Run No. 2) and 6090+50 (Seepage Run No. 3). A seepage analysis was not performed at station 6077+00 because the existing grade at this station is approximately 1395ft, which is likely outside the elevation of influence of the water in the Rocheleau Mine Pit. For the seepage analyses, it was assumed the mine pit on the north side of the Rocheleau pit was at an elevation of 1340 ft, while the water level on the south side (mining side) of the pit was at the elevation of the existing bedrock, approximately 1240 ft at stations 6082+50 and 6090+50 and 1200 ft at stations 6095+00. The hydraulic conductivity of the granular embankment fill was chosen as 3(10-5) ft/s, a typical value for a compacted granular material with less than 12% by dry weight passing the US No. 200 sieve (i.e. particles smaller than 0.075 mm). A value of 3(10-3) ft/s was chosen for the in-place mine waste rock material and embankment aggregate facing. This value was chosen based on the fact that this material will consist of boulder and gravel sized particles, which will likely result in the hydraulic conductivity at least two (2) orders of magnitude higher than the granular embankment fill material. Both these values need to be further evaluated for final design. Seepage pressures were input into the stability analyses. The results, shown in Figure Nos. 19, 20 and 21 are given in Table No. 11.



Table No. 11: Summary of Seepage Analysis Results at Design Cross Sections

Station

Embankment Side Slope

Angle

Slope Mid-height Bench

Included

Water Elevation

(ft)

Flow through Mine Waste

Rock Fill (gpm)*

Flow though Granular

Embankment (gpm)*

6082+50

60 degrees

No

1340ft – 1240ft 10gpm 0.25gpm

6095+00 45 degrees No 1340ft – 1200ft 14.5 gpm 0.23 gpm 6090+50

45 degrees

Yes

1340ft – 1240ft

10.2 gpm 0.46 gpm

*1 cfs = 7.48 gpm

Figure No. 19: Seepage Analysis No. 1: Station 6082+50

1290

1300 1310

1320

1330

Name: Reinforced Embankment Fill

Name: Mine Waste Rock Fill - Beneath Embankment Name: Mine Waste Rock Fill - Beneath Embankment

Water Surface Ele. = 1240ft


0 .0227 73 ft³/ sec

0.02

222 f

t³/se

c

Distance-400 -300 -200 -100 0 100 200 300 400

Elev

atio

n (x

100

0)

1.18

1.20

1.22

1.24

1.26

1.28

1.30

1.32

1.34

1.36

1.38

1.40

1.42

1.44

1.46

1.48

1.50

1.52

1.54

Total Flowrate through Roadway Embankment and Submerged Haul Road Embankment

Flowrate through Submerged Haul Road Embankment




126

0 1270

1280

128

0

1290

1300

131

0

1320

1330

1340

Name: Reinforced Embankment Fil l

Name: Bedrock Name: Bedrock

Name: Mine Waste Rock Fi l l - Beneath Embankmen

W ater Surface E le. = 1340ft

W ater Surface E le. = 1200ft

0.0

3291

8 ft³

/s ec

0.0

3240

4 ft³

/sec

Distance

-400 -300 -200 -100 0 100 200 300 400

Ele

vatio

n (x

100

0)

1.18

1.20

1.22

1.24

1.26

1.28

1.30

1.32

1.34

1.36

1.38

1.40

1.42

1.44

1.46

1.48

1.50

1.52

1.54


Name: Reinforced Embankment Fil l

Name: Mine Waste Rock Fi ll - Beneath Embankment Name: Mine Waste Rock Fil l - Beneath Embankment

12ft Bench added at Mid Slope Height



0.03 3082 ft³/se c

0.0

2277

4 ft³

/sec

Distance-400 -300 -200 -100 0 100 200 300

Ele

vatio

n (x

100

0)

1.18

1.20

1.22

1.24

1.26

1.28

1.30

1.32

1.34

1.36

1.38

1.40

1.42

1.44

1.46

1.48

1.50

1.52

1.54

The results of the seepage analysis indicates that the majority of the seepage flow, approximatley 97%, will occur through the in-place mine waste rock fill. The analysis shows the line of seepage will decrease through the granular fill embankment. 14.3 Stability Analysis of Proposed Roadway Embankment Constructed in the Dry Static and seismic embankment stability analyses were performed at the four (4) design cross section by analyzing the following failure modes: direct sliding at/near the reinforced granular embankment base, rotational failure within the reinforced granular embankment, and a compound failure through both the reinforced granular embankment and the submerged haul road embankment steepened side slope (global stability). The

Total Flowrate







analysis at each cross section includes a static analysis and a seismic analysis. A factor of safety for each failure mode at each cross section was calculated using a limit equilibrium method. In this method, a factor of safety against embankment instability is calculated based on the shear strength of the embankment fill and/or the foundation mine waste rock fill. As previously discussed in Section 14.2.1, the direct sliding and internal rotational failure modes were analyzed using the computer program ReSSA 2.0 by ADAMA Engineering, Inc. The global stability failure mode was analyzed using the computer program Slope-W by Geostudios, Inc. In addition, a Monte Carlo probability analysis was performed for select failure modes at select cross sections to assess the factor of safety in terms of soil strength parameter uncertainty and a numerical FLAC-Slope (Itasca) analysis was performed to assess zones of potential deformation. 14.3.1 Stability Analysis – Direct Sliding near Reinforced Embankment Base Direct sliding about the embankment base and/or along a lower layer of geosynthetic reinforcement was investigated for, Station 6082+50, Station 6090+50 and Station 6095+00. This failure mode involves the development of a failure plane due to the horizontal sliding of the embankment along its base or along a layer of geosynthetic reinforcement near the embankment base. The failure plane extends up into the embankment at an angle of approximately 45o + φ/2, where φ is the friction angle of the granular embankment. An interaction coefficient between the geosynthetic and the embankment fill material of 0.85 was used in the analysis. The analysis for Station 6090+50 included a 12 ft wide midslope bench on both sides of the embankment. Geosynthetic reinforcement with allowable tensile strengths, Tal, of 14,000 lb/ft, 7,000 lb/ft, and 5000 lb/ft, placed at various vertical increments and horizontal lengths were evaluated. The Rouchleau Pit water elevation was also varied between a static level of 1280 ft and 1320ft and a drawdown case of 1340 ft to 1240 ft. The Direct Sliding failure mode was evaluated considering both static and seismic conditions. The seismic stability analysis was performed assuming transverse PPAs of 0.3g and 0.15g. The vertical PPA component was assumed to be zero. A summary of the stability analysis results for the design stations are given in Table No. 12. A sampling of computer output files are included in Appendix. The results of the static and seismic stability analysis for a geosynthetic reinforced embankment at the three design cross sections indicates that to obtain the required minimum factor of safety of 1.3 for static conditions and 1.1 for seismic conditions, a geosynthetic reinforcement Tal of 14,000 lbs/ft placed at approximate 3 ft vertical intervals for each side slope, or a Tal of 7,000 lbs/ft, placed at 1.5 ft vertical intervals for each side slope is required if a seismic



coefficient of 0.3g is assumed. If a seismic coefficient of 0.15g is assumed, then a Tal of 7,000 lbs/ft placed at approximately 3 ft vertical intervals for each side slope or a Tal of 5,000 lbs/ft, placed at 1.5 ft vertical intervals for each side slope is required. As the Tal of the geosynthetic decreases, so does the cost of the product; however the labor to install double the number of layers is increased. The analysis also indicates that geosynthetic pull-out factor of safety of 1.3 is satisfied for the direct sliding failure mode, assuming a geosynthetic/fill interaction coefficient of 0.85. This is one of the outputs from the ReSSA computer program. For the 1H:1V (45 degree) embankment side slopes, a geosynthetic horizontal length of 115% of the embankment height is required. For the 1H:1.7V (60 degree) embankment side slopes, a geosynthetic horizontal length of 110% of the embankment height is required.



Table No. 12: Summary of Direct Sliding Failure Mode Analysis at Design Cross Sections

Run No. Station Failure Mode

Seismic Coeff. (g)

Geosynthetic Vertical Spacing*

(ft)

Geosynthetic Horizontal Length** (ft)

Water level (ft)

Tal (lb/ft) FS

Min FS*

1 6095+00 Direct Sliding 0.3 3ft 148ft (1.1H) 1280 14000 1.12 1.1

2 6095+00 Direct Sliding 0.3 3ft 148ft (1.1H) 1340 ‐ 1240 14000 1.12 1.1



5 6095+00 Direct Sliding Static 3ft 148ft (1.1H) 1280 7000 1.35 1.3 6 6095+00 Direct Sliding Static 3ft 148ft (1.1H) 1320 7000 1.34 1.3 7 6095+00 Direct Sliding 0.3 1.5ft 148ft (1.1H) 1280 7000 1.12 1.1

8 6095+00 Direct Sliding 0.3 1.5ft 148ft (1.1H) 1340 ‐ 1240 7000 1.12 1.1

9 6095+00 Direct Sliding 0.15 1.5ft 148ft (1.1H) 1340 ‐ 1240 5000 1.26 1.1

10 6095+00 Direct Sliding 0.15 1.5ft 148ft (1.1H) 1280 5000 1.26 1.1 11 6095+00 Direct Sliding Static 1.5ft 148ft (1.1H) 1280 5000 1.61 1.1 12 6095+00 Direct Sliding Static 1.5ft 148ft (1.1H) 1320 5000 1.56 1.3




16 6082+50 Direct Sliding 0.15 3ft 196ft (1.15H) 1280 7000 1.21 1.1 17 6082+50 Direct Sliding Static 3ft 196ft (1.15H) 1280 7000 1.57 1.3 18 6082+50 Direct Sliding Static 3ft 196ft (1.15H) 1320 7000 1.47 1.3




22 6090+50 Direct Sliding 0.15 3ft 165ft (1.1H) 1280 7000 1.17 1.1 23 6090+50 Direct Sliding Static 3ft 165ft (1.1H) 1280 7000 1.49 1.3 24 6090+50 Direct Sliding Static 3ft 165ft (1.1H) 1320 7000 1.4 1.3

* Reinforcing each side of the embankment ** H= Height of Reinforced Embankment



14.3.2 Stability Analysis –Rotational Failure within Reinforced Granular Embankment (Internal Rotation) A rotational failure surface within the reinforced granular embankment was investigated at the four embankment cross sections. Geosynthetic reinforcement, with allowable tensile strengths of 14,000 lb/ft, 7,000 lb/ft, and 5000 lb/ft placed at various vertical increments and horizontal lengths was evaluated. The Rouchleau pit water elevation was also varied between a static level of 1280 ft and 1320 ft and a drawdown case of 1340 ft to 1240 ft in the analysis at each design station. This failure mode was evaluated considering both static and seismic conditions. The seismic stability analysis was performed assuming a transverse PPAs of 0.3g and 0.15g. The vertical PPA component was assumed to be zero. The analysis for Station 6090+50 also involved a 12ft wide midslope bench on both sides of the embankment. A summary of the stability analysis results for the design stations are given in Table No. 13. A sampling of computer output files are included in Appendix. The results of the static and seismic stability analysis for a geosynthetic reinforced embankment at the design cross sections indicates that to obtain the required minimum factor of safety of 1.3 for static conditions and 1.1 for seismic conditions, a geosynthetic reinforcement Tal of 14,000 lbs/ft placed at 3 ft vertical intervals for each side slope, or a Tal of 7,000 lbs/ft placed at 1.5 ft vertical intervals for each side slope are required if a seismic coefficient of 0.3g is assumed. If a seismic coefficient of 0.15g is assumed, then a Tal of 7,000 lbs/ft, placed at 3 ft vertical intervals for each side slope or a Tal of 5,000 lbs/ft, placed at 1.5 ft vertical intervals for each side slope is required. This is the same result as the direct sliding analysis. For the design cross section with 1H:1V (45 degree) embankment side slopes a geosynthetic horizontal length of 115% of the embankment height (1.15H), is required. For the design cross sections with 1H:1.7V (60 degree) embankment side slopes a geosynthetic horizontal length or 110% of the embankment height (1.1H), is required.



Table No. 13: Summary of Internal Rotational Failure Mode Analysis at Design Cross Sections


Seismic Coeff. (g)

Geosynthetic Vertical

Spacing* (ft)

Geosynthetic Horizontal Length (ft)

Water level (ft)

Tal (lb/ft) FS

Min FS

25 6095+00 Internal Rotation 0.3 3ft 148ft 1280 14000 1.19 1.1

26 6095+00 Internal Rotation 0.3 3ft 148ft 1340 ‐ 1240 14000 1.19 1.1


28 6095+00 Internal Rotation 0.15 3ft 148ft 1280 7000 1.19 1.1 29 6095+00 Internal Rotation Static 3ft 148ft 1280 7000 1.43 1.3 30 6095+00 Internal Rotation Static 3ft 148ft 1320 7000 1.37 1.3 31 6095+00 Internal Rotation 0.3 1.5ft 148ft 1280 7000 1.19 1.1

32 6095+00 Internal Rotation 0.3 1.5ft 148ft 1340 ‐ 1240 7000 1.19 1.1

33 6095+00 Internal Rotation 0.15 1.5ft 148ft 1340 ‐ 1240 5000 1.28 1.1

34 6095+00 Internal Rotation 0.15 1.5ft 148ft 1280 5000 1.28 1.1 35 6095+00 Internal Rotation Static 1.5ft 148ft 1280 5000 1.53 1.1 36 6095+00 Internal Rotation Static 1.5ft 148ft 1320 5000 1.47 1.3




40 6082+50 Internal Rotation 0.15 3ft 196ft 1280 7000 1.12 1.1 41 6082+50 Internal Rotation Static 3ft 196ft 1280 7000 1.37 1.3 42 6082+50 Internal Rotation Static 3ft 196ft 1320 7000 1.47 1.3




46 6090+50 Internal Rotation 0.15 3ft 165ft 1280 7000 1.12 1.1 47 6090+50 Internal Rotation Static 3ft 165ft 1280 7000 1.34 1.3 48 6090+50 Internal Rotation Static 3ft 165ft 1320 7000 1.30 1.3

* Reinforcing each side of the embankment



14.3.3 Stability Analysis – Compound Failure through Both Reinforced Granular Embankment and Mine Waste Rock (Global Stability) A compound failure mode, extending through the reinforced granular embankment and extending through a portion of the submerged haul road embankment was investigated at Stations 6090+50 and 6095+00. Geosynthetic reinforcement, with Tal of 14,000 lb/ft 7,000 lb/ft, and 5000 lb/ft placed at various vertical increments and horizontal lengths was evaluated. The Rouchleau pit water elevation was also varied between a static water level of 1320ft and 1280ft and a drawdown case of 1340ft to 1240ft., as was evaluated for the other failure modes. The analysis for Station 6090+50 also involved a 12ft wide midslope bench on both sides of the embankment. This compound or global failure mode was evaluated considering both static and seismic conditions. The seismic stability analysis was performed assuming a transverse PPAs of 0.3g and 0.15g. The vertical PPA component was assumed to be zero. A summary of the stability analysis results for the design stations are given in Table No. 14. A sampling of the computer output files are included in Appendix. The results of the static and seismic stability analysis for a geosynthetic reinforced embankment at the design cross sections indicates that to obtain the required minimum factor of safety of 1.3 for a static condition and 1.1 for seismic condition, a geosynthetic reinforcement Tal of 14,000 lbs/ft placed at 3 ft vertical intervals for each side slope, or a Tal of 7,000 lbs/ft, placed at 1.5 ft vertical intervals for each side slope are required if a seismic coefficient of 0.3g is assumed. If a seismic coefficient of 0.15g is assumed then a Tal of 7,000 lbs/ft, placed at 3 ft vertical intervals for each side slope or a Tal of 5,000 lbs/ft, placed at 1.5 ft vertical intervals for each side slope is required. A geosynthetic horizontal length of 110% of the embankment height (1.1H) is required. This is the same result as the previous Direct Sliding and Internal Rotation analyses. For the design cross sections at Stations 6090+50 and 6095+00, we assessed a 1H:1.7V (60 degree) embankment side slope since it resulted in an embankment footprint which would fit on the narrow submerged haul road embankment width at these sections.



Table No. 14: Summary of Compound Global Stability Failure Mode Analysis at Design Cross Sections


Seismic (g)


Spacing* (ft)

Geosynthetic Horizontal Length**

(ft) Water level

(ft) Tal

(lb/ft) FS Min FS

49 6095+00 Global 0.3 3ft 148ft (1.1H) 1340 ‐ 1240 14000 1.35 1.1 50 6095+00 Global 0.3 3ft 148ft (1.1H) 1280 14000 1.25 1.1 51 6095+00 Global 0.15 3ft 148ft (1.1H) 1340 ‐ 1240 7000 1.66 1.1 52 6095+00 Global 0.15 3ft 148ft (1.1H) 1280 7000 1.51 1.1 53 6095+00 Global Static 3ft 148ft (1.1H) 1280 7000 2.18 1.3 54 6095+00 Global Static 3ft 148ft (1.1H) 1320 7000 2.18 1.3 55 6095+00 Global 0.3 1.5ft 148ft (1.1H) 1340 ‐ 1240 14000 1.31 1.1 56 6095+00 Global 0.3 1.5ft 148ft (1.1H) 1280 14000 1.18 1.1 57 6095+00 Global 0.15 1.5ft 148ft (1.1H) 1340 ‐ 1240 5000 1.69 1.1 58 6095+00 Global 0.15 1.5ft 148ft (1.1H) 1280 5000 1.59 1.1 59 6095+00 Global Static 1.5ft 148ft (1.1H) 1280 5000 2.3 1.3 60 6095+00 Global Static 1.5ft 148ft (1.1H) 1320 5000 2.33 1.3

61 6090+50 Global 0.3 3ft 165ft (1.1H) 1340 ‐ 1240 14000 1.33 1.1 62 6090+50 Global 0.3 3ft 165ft (1.1H) 1280 14000 1.14 1.1 63 6090+50 Global 0.15 3ft 165ft (1.1H) 1340 ‐ 1240 7000 1.3 1.1 64 6090+50 Global 0.15 3ft 165ft (1.1H) 1280 7000 1.66 1.1 65 6090+50 Global Static 3ft 165ft (1.1H) 1280 7000 2.14 1.3 66 6090+50 Global Static 3ft 165ft (1.1H) 1320 7000 2.11 1.3

* Reinforcing each side of the embankment ** H=Height of Reinforced Embankment The results of the static and seismic limit equilibrium stability analyses indicate that the minimum factors of safety with regard to internal rotation, direct sliding and compound failure surfaces can be met with a back-to-back geosynthetic reinforced embankment at the three design cross sections. The stability analysis results indicate that the seismic analysis will govern the embankment reinforcement design. The direct sliding mode of failure tended to produce the lower factors of safety compared to the other failure modes. The results for the seismic analysis indicate that the geosynthetic strength and geometric characteristics is dependant on the design seismic coefficient and the sideslope angle. A summary of the geosynthetic strength and geometric characteristics relative to the design station and seismic coefficient are given in Table No. 15.



Table No. 15: Reinforced Embankment Geosynthetic Requirements at Design Cross Sections

Design Station

Sideslope Angle

Seismic coefficient

Geosynthetic Tal (lb/ft)


Increment *(ft)

Geosynthetic Horizontal

Length **(ft)

6082+50 45 deg. (1H:1V)

0.3g 14,000 3ft 1.15H

6082+50 45 deg. (1H:1V)

0.15g 7,000 3ft 1.15H

6095+00 60 deg. (1H:1.7V)

0.3g 14,000 3ft 1.10H

6095+00 60 deg. (1H:1.7V)

0.15g 7,000 3ft 1.10H

6095+00 60 deg. (1H:1.7V)

0.15g 5,000 1.5ft 1.10H

6090+50 60 deg. (1H:1.7V)

0.3g 14,000 3ft 1.10H

6090+50 60 deg. (1H:1.7V)

0.15g 7,000 3ft 1.10H

6090+50 60 deg. (1H:1.7V)

0.15g 5,000 1.5ft 1.10H

* Reinforcing each side of the embankment ** H=Height of Reinforced Embankment 14.3.4 Seismic Stability Evaluation using Monte Carlo Probability Analysis A seismic stability analysis was performed at three design stations (6082+50, 6090+50 and 6095+00) using a Monte Carlo probability analysis. This analysis uses the uncertainty of the strength parameters associated with the proposed reinforced embankment fill and with the in-place mine waste rock fill to estimate the variability of the factor of safety. The analysis then estimates the probability that the factor of safety for that failure mode analyzed will be less than 1.0 based on the uncertainty in the strength parameters. The Direct Sliding and Global failure modes were chosen for the Monte Carlo analysis because the limit equilibrium analysis indicated that the lower factors of safety resulted from these failure modes. The estimated uncertainty of the embankment fill and mine waste rock fill strength properties was quantified in Section 14.2.2. The input parameters for this evaluation were similar to those used for the limit equilibrium analysis including a transverse PPA of 0.3g. The embankment cross section



at Station 6090+50 included a 12 ft wide midslope bench. The geosynthetic reinforcement strength was assumed to be 14,000 lb/ft placed in 3 ft vertical increments at lengths of either 1.15H for each side slope for the 1H:1V (45 degree) embankment design section and 1.1H for each side slope for the 1H:1.7V (60 degree) embankment design sections, where H=Height of the Reinforced Embankment. The analysis was performed assuming a static water level of 1280 ft. A summary of the results for the Monte Carlo simulations are given in Table No. 16. A sampling of the computer outputs is included in the Appendix.

Table No. 16: Results of Monte Carlo Seismic Stability Simulations Run No.

Station Failure Mode Parameter Varied Parameter Mean*

Parameter Standard Dev.*

Mean Factor of Safety

Factor of Safety Range**

Probability of Failure (FS<1.0)

1 6082+50 Direct Sliding at Base

Embankment Fill Friction Angle

35 deg 2 deg 1.11 0.84 – 1.32

4.0%



35 deg 2 deg 1.10 0.87 – 1.36

2.4%



35 deg 2 deg 1.16 1.01 – 1.42

0.0%

4

6095+00 Compound (Global) Failure


35 deg 2 deg 1.25

1.12 – 1.37

0.0%

5 6095+00 Compound (Global) Failure

Mine Waste Rock Fill Friction Angle

43 deg 3.5 deg 1.24 0.90 – 1.55

0.2%

*From Report Section 14.2.2 **Considering normal distribution and five (5) standard deviations from the mean The results identify that the greatest probability of failure occurs for the 170ft high embankment at Station 6082+50, if the embankment fill material friction angle is 35 degrees +/- 2 degrees. (1 standard deviation). This identifies that it will be important to have quality control of the embankment fill material during placement and compaction. The analysis also indicates that failures through the mine waste rock fill (Run Nos. 4 &5) have a lower (0.0% to 0.2%) probability of failure, provided the friction angle is as assumed. 14.3.5 Seismic Stability Evaluation using Shear Displacement Modeling A seismic stability analysis was performed at Stations 6082+50 and 6095+00 using FLAC modeling to indicate the location of the strain that may be experienced within the proposed embankment during a blasting event. The input parameters for the FLAC/Slope analysis were the same as for the limit equilibrium analysis, including a transverse PPA of 0.3g. The geosynthetic reinforcement, with a Tal of 14,000 lb/ft was placed in 3ft



vertical increments at horizontal lengths of 176ft (1.15H) for each side slope at station 6082+50 and horizontal lengths of 148ft (1.1H) for each side slope at station 6095+00. The static water level for this analysis was assumed to be at an elevation of 1280 ft. The results of the FLAC/Slope seismic stability analysis at station 6082+50 (170ft high embankment), given in Figure No. 22, indicate the development of the shear strains. The darker colors on Figure No. 22 show the higher areas of strain. The maximum strain develops approximately at the opposite crest of the embankment and extends down to daylight approximately 50 ft below and 50 ft out from the embankment toe. This strain develops at a factor of safety of 1.5; which is well above the FHWA seismic minimum of 1.1.

Figure No. 22: FLAC-Slope Seismic Stability Analysis at Station 6082+50

The results of the FLAC/Slope seismic analysis at station 6095+00 (135ft high embankment), given in Figure No. 23, indicates the development of shear strains. The maximum shear strain develops in the lower portion of the embankment and extends down to daylight out approximately 100ft below and 100ft out from the embankment toe. This strain occurs at a factor of safety of 1.21, which is above the minimum FHWA –seismic factor of safety of 1.1.



In terms of the magnitude of the strain identified in Figure Nos. 22 and 23, the model was not calibrated for strain magnitude; in order to predict strain magnitude we recommend a testing program to assess the modulus and Poisson’s ratio for the selected embankment fill and the selected geosynthetic reinforcement. In any event, these higher strain locations should be instrumented and monitored during construction for movement.

Figure No. 23: FLAC-Slope Seismic Stability Analysis at Station 6095+00

14.4 Submerged Haul Road Embankment Steepened Side Slope Stability The in-situ submerged haul road embankment contains side slope angles of approximately 1.3H:1V at heights ranging approximately from 80 - 100ft. Based on the MnDOT bathymetric survey and the U.S. Steel Corporation embankment cross sections, the steepened side slopes exist on both the north and south sides of the submerged haul road embankment approximately between stations 6087+00 and 6098+00. A stability analysis was performed at Station 6095+00 where the estimated steepened embankment side slopes are approximately 80 ft in height. The strength of the mine waste rock (friction angle) was modeled based on Figure Nos. 13 and 14 presented in Section No. 8.3. The seismic stability analysis of the submerged haul road embankment was further evaluated to estimate a minimum “clear” distance between the proposed reinforced embankment toe and the outside crest of the mine waste rock fill embankment where the

1.21

Mine Waste Rock with Side Slope of 1.3H:1V

Embankment Toe

Crest of Submerged Haul Road Embankment

100ft Clear Distance



steepened side slopes exist. The results of the seismic stability analysis indicate that a clear distance of 100ft and 40ft results in a factor of safety of 1.2 and 1.1, respectively, against side slope instability during a seismic event with a transverse PPA = 0.3g and assuming a static water level within the mine pit of 1280 ft. If seepage pressures are present within the submerged haul road embankment during a blasting event, the factor of safety of 1.1 is reduced to 1.08. The results of this stability analysis are given in Table No. 17. A representative output is given in Figure No. 24. A sampling of the output results is included in the Appendix.

Table No. 17: Results of Station 6095+00 Submerged Haul Road Steepened Side slope Stability*

Run No.

Mine Waste Rock

Embankment Height (ft)

Mine Waste Rock

Embankment Sideslopes

Analysis Seismic Coeff. (xg)

Search Criteria

RouchleauPit Water Level (ft)

Factor of Safety

67 80ft 1.3H:1V Seismic 0.3 Global Stability

1340ft – 1240ft

1.07


1280ft 1.12


1320ft 1.10

70

80ft 1.3H:1V Seismic 0.3 Global Stability

1200ft 1.36

71 80ft 1.3H:1V Static - Global Stability

1320ft 2.34

*40ft “clear” distance from embankment toe to outside crest edge of submerged haul road embankment



Figure No. 24: Submerged Haul Road Embankment Steepened Side slope Seismic Stability Analysis

1.069

Bedrock

Name:Unit WPhi Fn

Mine Waste Rock Fill Angle of Internal FrictionReduced in 10ft Depth incrementsReduction based on Developed Strength Model

40ft

Phi = 60 deg

Phi = 51 degPhi = 49 deg

Phi = 48 degPhi = 47.5 degPhi = 46.5 deg

Phi = 46 deg

Submerged Haul Road Embankment Steepened Slope Stability Analysis

Distance-380 -360 -340 -320 -300 -280 -260 -240 -220 -200 -180 -160 -140 -120

Elev

atio

n (x

100

0)

1.181.191.201.211.221.231.241.251.261.271.281.291.301.311.32

14.5 Mine Waste Rock/Bedrock Weakened Interface Stability Analysis A seismic stability analysis was performed at Station 6095+00 where the proposed reinforced granular embankment will be at a height of approximately 135 ft with side slopes of 1H:1.7V (60 degree) and where the proposed reinforced embankment toe will be located near to steepened slopes on both the north and south sides of the submerged haul road embankment. This analysis considered the possibility of a weakened interface present between the mine waste rock fill within the submerged haul road embankment and the bedrock below. Though no such weakened interface layer was detected either in the borings or by the resistivity survey, we postulate that sand sized particles could migrate down through the mine waste rock fill and result in a layer of sand at the bedrock interface. The weakened interface between the mine waste rock fill and the bedrock was given an angle of internal friction of 35 degrees. This value was chosen relative to value of the mine waste rock fill (41.5 to 43 degrees). The analysis was performed to determine that if this weakened interface was present, then at what elevation and orientation could this weakened interface have an effect on the stability of the proposed embankment. As shown in Figure No. 25, the horizontal extent and the elevation of the weakened interface was varied. The stability analysis assumed 1H:1.7V (60 degree) embankment side slopes, geosynthetic reinforcement, Tal = 14,000 lb/ft, at 3 ft horizontal spacing for each side slope and with a phreatic surface varying from 1340 ft to 1200 ft across the embankment.



A friction angle of 35 degrees was assumed for the reinforced embankment fill and at values ranging from 41.5 to 60 degrees was assumed for the mine waste rock fill. These are the same values used for the seismic and static stability evaluation presented in Section 14.3. The seismic stability analysis was performed assuming a transverse PPA of 0.3g. The vertical PPA component for the seismic analysis was assumed to be zero. It was found that the potential weakened interface did not have a significant effect on the static stability of the proposed roadway embankment. The results of the weakened interface analysis indicate that:

• If a weakened interface is present, it could result in a seismic factor of safety in the range of 1.1 (acceptable per FHWA) if the interface plane was horizontal and if it extends continuously from beneath the center of the embankment to within 20 ft of the mine waste rock fill edge of slope.

• The seismic factor of safety did not significantly vary regardless of the horizontal elevation of the weakened interface. The weakened interface was assumed at elevations 1240 ft and 1200 ft.

• Lower factors of safety occurs when there are seepage pressures present in the submerged haul road embankment, however, the seismic factor of safety remains greater than 1.1 acceptable per FHWA.

Figure No. 25: Station 6095+00 Potential Weakened Interface Seismic Stability Analysis, Interface Elevation at 1200 ft and terminating 20 ft Prior to Slope Face

1.197

135ft High Embankment Height (Station 6095+00)60 degree slope Embankmend SideslopesGeogrid Reinforcement LTDS = 14,000 lb/ftGeogrid Length = 1.1*H = 148.5ftSeismic Coeff = Value: 0.3g

Name: Reinforced Embankment Fi ll Unit W eight: 135 pcfPhi: Multiple T rial: 35 °

Name: Reinforced Embankment Fi ll

Name: Reinforced Embankment Fi ll

Name: Mine W aste Rock Material - Outs ide Embankment Unit Weight: 170 pcfPhi Fn: Mine Waste Rock - Outs ide Embankment

Name: Mine Waste Rock Material - Outs ide Embankment Unit Weight: 170 pcfPhi Fn: Mine W aste Rock - Outs ide Embankment

Distance-400 -300 -200 -100 0 100 200 300 400

Ele

vatio

n (x

100

0)

1.18

1.20

1.22

1.24

1.26

1.28

1.30

1.32

1.34

1.36

1.38

1.40

1.42

1.44

1.46

1.48

1.50

1.52

1.54

Failure Plane

Weakened Interface

Bedrock



15.0 ANALYSIS – EMBANKMENT CONSTRUCTION IN WET CONDITIONS A slope stability analysis was performed at Station 6095+00 assuming that the lower 25 ft, from elevation from elevation 1305 ft to 1280 ft, of the embankment was constructed by placing fill into standing water. Placing fill into water will prevent geosynthetic reinforcement from being placed in this zone. The portion of the embankment constructed underwater was assumed to have 2H:1V side slopes. Though not analyzed, a rock buttress will be required over the 2H:1V underwater placed fill side slopes to resist shallow sloughs that could occur both statically and as a result of a mine blast. The following applicable deeper seated failure modes were used in the analysis: direct sliding through underwater fill at embankment base (direct sliding), rotational failure plane development within the reinforced embankment and underwater fill (internal rotational failure), and a compound failure through the reinforced embankment, underwater fill and the submerged haul road embankment steepened side slope (global stability).The analysis includes a static analysis and a seismic analysis. A factor of safety for each failure mode at each cross section was calculated using a limit equilibrium method. In this method, a factor of safety against embankment instability is calculated based on the shear strength of the embankment fill, underwater fill and potentially the mine waste rock fill. The three failure modes were analyzed using the computer program Slope-W by Geostudios, Inc. Static and seismic stability analyses were performed in substantial accordance with FHWA-NHI-10-025. The Spencer method of limit equilibrium analysis was used. This method analyzes potential circular or edge shear surfaces by separating the soil above the proposed failure plan into multiple segments and then uses both force and moment or moment equilibrium to balance the forces in each segment. In the case of the seismic analysis, a pseudo-static seismic force was induced on the embankment to simulate a blasting event. In addition, a Monte Carlo probability analysis was performed for select failure modes to assess the factor of safety in terms of soil strength parameter uncertainty. The input parameters for the Monte Carlo simulations performed for this analysis are indicated in Table No. 18. A typical factor of safety output in the form of a normal distribution is given in Figure No. 27.



Table No. 18: Monte Carlo Statistical Analysis Input Parameters

Parameter Mean

(deg) Standard

Dev. (deg) Min. Value*

(deg) Max. Value *

(deg)

Underwater Fill Material 30 3 15 45 *Minimum and Maximum values are Calculated based on 5 Standard Deviations from the Mean 15.1 Material Strength Parameters used in Analysis For this analysis, the mine waste rock and reinforced embankment fill material properties used were the same as those used in the Stability Analysis performed in Section 14.2. The underwater fill material was assumed to be a well-graded aggregate material created by screening/crushing the on-site Mine Waste Rock Fill. It was assumed that this material would be placed into standing water and would be uncompacted. The density and angle of internal friction of the underwater placed fill was assumed to be 120 pcf and 30 degrees, respectively. These values are for a granular-type fill; not crushed mine rock fill. The geosynthetic reinforcement strength, horizontal length and vertical offset were the same as evaluated for the reinforced embankment constructed in the dry analysis, however no reinforcement was included in the lower 30 ft of the embankment. 15.2 Stability Analysis – Station 6095+00, Underwater Fill Placement Slope stability was evaluated considering both static and seismic conditions at station 6095+00 for a case where no geosynthetic reinforcement is included in the lower 30ft of the embankment, since this fill would be placed into water. The seismic stability analysis was performed assuming a transverse PPA of 0.3g and 0.15g. The vertical PPA component was assumed to be zero. Geosynthetic reinforcement, with allowable tensile strengths of 14,000 lb/ft and 10,300 lb/ft placed at various vertical increments and horizontal lengths were considered. The Rouchleau pit water elevation was also varied between static water levels of 1280ft and 1320ft. A summary of the stability analysis results for Station 6095+00 is given in Table No. 22. A sampling of computer output files are included in the Appendix. The results of the static and seismic stability analysis identify that to obtain the required minimum factor of safety of 1.3 - static and 1.1 – seismic for a deeper seated failure, a geosynthetic reinforcement Tal of 14,000 lbs/ft placed at 1.5ft vertical increments for each side slope in the lower half of the reinforced portion (from elevation 1310ft to 1365ft) of the embankment and at 3 ft vertical intervals for each side slope in the upper half of the reinforced portion (from elevation 1365ft to 1420ft) of the embankment is required. If a seismic coefficient of 0.15g is considered to be the maximum PPA observed in the



embankment, a geosynthetic reinforcement Tal of 10,300 lbs/ft placed at 1.5ft vertical increments for each side slope in the lower half of the reinforced portion of the embankment and at 3 ft vertical intervals for each side slope in the upper half of the reinforced portion of the embankment will meet the minimum safety factors. A geosynthetic horizontal length of 115% of the embankment height (1.15H) is required. The results of the stability analysis are given in Table No. 19. The result of a Direct Sliding failure mode analysis is given in Figure No. 26. A rock buttress, with a higher friction angle than 30 degrees, will be required over the 2H:1V underwater placed granular fill to resist shallow sloughs during both static conditions and during a mine blast. Once this material is selected, a stability analysis should be performed.



Table No.19: Summary of Stability Analysis for Lower Portion of Embankment

Constructed in Wet Conditions

Run No.

Station Geosynthetic Length (ft)

Geosynthetic Vert. Increment (ft)

Geosynthetic Tal (lbs/ft)

Failure Mode

Seismic Coeff. (xg)

Pit Water Level (ft)

FS FS Min.

72 6095+00 155ft (1.15H) Lower Half 1.5ft, Upper Half 3ft

14,000 Direct Sliding

0.3 1280ft 1.15 1.1



0.15 1280ft 1.20 1.1



Static 1280ft 1.75 1.3



Static 1320ft 1.65 1.3

76 6095+00 155ft (1.15H) Lower Half 1.5ft,

Upper Half 3ft 14,000 Internal

Rotational 0.3 1280ft 1.18 1.1

77 6095+00 155ft (1.15H) Lower Half 1.5ft,


Rotational 0.15 1280ft 1.45 1.1

78 6095+00 155ft (1.15H) Lower Half 1.5ft,


Rotational Static 1280ft 1.88 1.3

79 6095+00 155ft (1.15H) Lower Half 1.5ft,


Rotational Static 1320ft 1.94 1.3


14,000 Global Stability

0.3 1280ft 1.12 1.1

81 6095+00 155ft (1.15H) Lower Half 1.5ft,

Upper Half 3ft 10,300 Global

Stability 0.15 1280ft 1.41 1.1

82 6095+00 155ft (1.15H) Lower Half 1.5ft,


Stability Static 1280ft 1.95 1.3

83 6095+00 155ft (1.15H) Lower Half 1.5ft,


Stability Static 1320ft 1.92 1.3



Figure No. 26: Station 6095+00, with Lower Portion of the Embankment Constructed Underwater, Direct Sliding Failure Mode, Seismic Coeff. = 0.3g

1.115

115ft High Embankment Height (Station 6095+00)60 degree slope Embankmend SideslopesGeogrid Reinforcement LTDS = 14000 lb/ftGeogrid Length = 1.15*H = 155ft25ft Fi ll Placed Underwater to Ele 1310ftSeismic Coeff = Value: 0.3g

Name: Reinforced Embankment Fi l l Unit W eight: Multiple T rial : 135 pcfPhi: 35 °

Name: Bedrock

Name: Mine W aste Rock Material - Outs ide Embankment

Name: Mine W aste Rock Fil l - beneath embankment Unit W eight: 170 pcfPhi Fn: Mine Waste Rock - Beneath Embankment

Name: Mine W aste Rock Material - Outs ide Embankment Unit W eight: 170 pcfPhi Fn: Mine Waste Rock - Outs ide Embankment

Name: Underwater Fil l Unit W eight: 130 pcfPhi: 30 °

2H:1V Underwater Sideslopes

Geogrid Reinforc ement Spacing @1.5ft in Lower Half of Embankment3ft Vertical Spac ing in Upper Half of Embankment

Distance-400 -300 -200 -100 0 100 200 300 400

Ele

vatio

n (x

100

0)

1.18

1.20

1.22

1.24

1.26

1.28

1.30

1.32

1.34

1.36

1.38

1.40

1.42

1.44

1.46

1.48

1.50

1.52

1.54

15.3 Station 6095+00, Underwater Fill Placement, Seismic Stability Evaluation using Monte Carlo Probability Analysis A seismic stability analysis was performed at design station 6095+00 using a Monte Carlo probability analysis. This analysis uses the uncertainty of the underwater fill strength parameters to estimate the variability of the factor of safety with respect to a deeper seated compound sliding failure though the underwater placed fill and the geosynthetic reinforced embankment above. The analysis can then estimate the probability that the factor of safety will be less 1.0. The estimated uncertainty of the underwater fill strength properties was quantified in Section 15.1 – Table No. 18. The input parameters for this evaluation were similar to those used for the limit equilibrium analysis, a transverse PPA of 0.3g was assumed and the vertical PPA component was assumed to be zero. No reinforcement in the lower 30ft of the embankment was assumed. The geosynthetic reinforcement strength was assumed to be 14,000 lb/ft, placed in 1.5ft vertical intervals for each side slope for the lower half of the reinforced portion of the embankment and 3ft vertical increments for each side slope for the upper half of the reinforced portion of embankment. The reinforcement was placed at horizontal lengths of 1.15H for the 1H:1.7V (60 degree) side slope design section. The analysis was performed assuming a static water level of 1280ft. A summary of the results for the Monte Carlo simulations are given in Table No. 12. A sample normal factor of safety output distribution is given in Figure No. 27. The results are given as Monte Carlo Simulation No. 6.



Table No. 20: Result of Monte Carlo Simulation for Station 6095+00, Base of

Embankment Constructed in the Wet

*From Section 15.0 – Table No. 18 ** Considering Normal Distribution and 5 standard deviations from the mean Figure No. 27: Factor of Safety Gaussian Normal Distribution Calculated from the Monte

Carlo Simulation Run No. 6

Probability Density Function

Freq

uenc

y (%

)

Factor of Safety

0

10

20

30

0.909 0.949 0.989 1.029 1.069 1.109 1.149 1.189 1.229 1.269

The results of the Monte Carlo statistical analysis for the direct sliding failure mode indicate that based on the estimated variability in the angle of internal friction of the underwater fill, the factor of safety can range approximately from 0.94 to 1.2. The probability of embankment failure (factor of safety less than 1.0) was determined to be 0.2% considering a standard deviation of 3 degrees from the friction angle. This indicates that the variability in the underwater placed fill angle of internal friction must be reduced to a standard deviation less than 3. A testing program of potential underwater fill sources and a comprehensive material specification would be required in order to reduce the variability in the angle of internal friction. 15.4 Summary of Stability Analysis Station 6090+50, Lower 30ft of Embankment Constructed in the Wet without Geosynthetic Reinforcement A minimum seismic factor of safety of about 1.1 was calculated for direct sliding and global stability for the lower portion of the embankment constructed in the wet and when

Run No.

Failure Mode

Seepage Forces/Static Water Level

Parameter Varied

Parameter Mean*

Parameter Sta. Dev.*

Mean Factor of Safety

Factor of Safety Range**

Probability of Failure (FS<1.0)**

6 Direct Sliding at Base

Static Water Level = 1280ft

Underwater Fill Friction Angle

30 deg 3 deg 1.13 0.94 – 1.23

0.21%



a transverse PPA of 0.3g is applied for deeper seated failures. This factor of safety meets the minimum FHWA guidance. The results of the Monte Carlo statistical analysis indicate that for direct sliding about the base of the embankment through the underwater fill material, that based on the estimated uncertainty in the strength properties of the underwater fill material, a 0.2% chance of failure was calculated when a transverse PPA of 0.3g is applied to the embankment. This result indicates that the fill (and specifically the shear strength) of the material to be placed into standing water needs to be further evaluated by a testing program and a comprehensive specification developed that reduces material variability. Shallow sloughs of the side slope could occur which could lead to a deeper seated failure, if an appropriate rock buttress is not placed. Once the underwater fill soil is chosen, then a stability analysis would be required in order to design the underwater cross section including the rock buttress 16.0 ANALYSIS – CONSTRUCTION WITH LEVEE OR GEOTEXTILE TUBE COFFERDAM FOR LOCALIZED DEWATERING 16.1 Localized Dewatering Seepage Analysis A seepage analyses was performed on both sides of the submerged haul road embankment considering a temporary levee system was installed for localized dewatering of the construction zone. The levee system could be constructed using either rockfill levees pushed into standing water or using large diameter geotextile tubes filled with sand. A semi-pervious to impervious type of liner would likely need to be placed to reduce underseepage coming up into the construction zone. Based on an average submerged haul road crest elevation of 1280ft, we assumed that the dewatering would occur down to an elevation of 1275ft. Based on the August, 2013 Rouchleau Pit water elevation, 1305.1ft, the water would need to be initially drawn down 30ft, with a 30ft head difference maintained for the initial portion of construction. The height of the perimeter levees would be need to be at least 25ft, plus an estimated 3 – 4ft of free board to allow for wave action and Pit water level variation during construction. The seepage analysis was performed to estimate the pumping flowrate that would be required to dewater and maintain relatively dry conditions at the base of the proposed roadway embankment. The analysis considered that the embankment would be constructed with 1H:1.7V (60 degree) side slopes and 10ft of clearzone between the toe of the proposed roadway embankment and the inside toe of the levee system. This would require an approximately 320ft wide area that would need to be dewatered for the proposed roadway embankment construction.



For this seepage analysis, the hydraulic conductivity of a granular type levee was chosen as 3(10-5) ft/s (0.001 cm/s). A value of 3(10-3) ft/s (0.1 cm/s) was estimated for the mine waste rock material. This levee value was chosen considering the hydraulic conductivity to be at least two (2) orders of magnitude lower than the hydraulic conductivity of the mine waste rock fill. These are the same values the were used for the seepage analysis associated with the stability analyses in Section 14. These parameters were varied to assess the potential variability in the required pumping rate. The hydraulic conductivity of the mine waste rock fill material was increased and decreased one order of magnitude, from 3(10-3) ft/s (0.1 cm/s) to 3(10-2) ft/s 1.0 cm/s and 3(10-4) ft/s (0.001 cm/s). The results of the seepage analysis indicate that to accommodate a 30ft head difference between the pit water level and the construction zone, an approximate pumping rate of 54 gpm/ft will be required assuming a hydraulic conductivity of the mine waste rock fill material of 3(10-3) ft/s (0.1 cm/s). This would require a pumping flowrate of approximately 27,000 gpm per 500ft of dewatered length, considering a 320ft wide construction zone. The seepage analysis indicates that approximately 96% of the seepage flow rate results from underseepage. As shown in Table No. 21, the seepage flowrate is dependent on the hydraulic conductivitiy of the mine waste rock fill, as an order of magnitude difference in the mine waste rock hydraulic conductivity results in an order of magnitude difference in the seepage flowrate. A sample seepage analysis result from SeepW is given in Figure No. 28. The results indicate that if a levee cofferdam is to be considered, that a comprehensive evaluation be implemented in order to determine the in-situ hydraulic conductivity of the mine waste rock fill within at least 50ft of the surface of the submerged mine haul road crest. Slug testing is proposed to be performed in conjunction with IDEA Drilling, Inc. work off a barge in the Spring of 2014.

Table No. 21: Summary of Seepage Flow Rates based for Localized Dewatering

Seepage Analysis

Rouchleau Pit Water Level (ft)

Dewatering Elevation

(ft)

Mine Waste Rock

Permeability (cm/s)

Geotextile Tube

Permeability (cm/s)

Seepage Flowrate (gpm/ft)

Estimated Pumping per 500ft

of Dewatering

4 1305 1275 0.1 0.001 54 27,000 5 1305 1275 0.1 0.01 54 27,000 6 1305 1275 1.0 0.01 540 270,000 7 1305 1275 0.01 0.01 5.4 2,700



Figure No. 28: Flownet from Seepage Analysis No. 4

Seepage Analysis - Station 6095+00Dew atering using Perimeter GeotubesGeotubes in 4,3,2,1 Configuration Mine Waste ROck Permeability = 0.1cm/sLevee Permeability = 1e-3 cm/s

Rocheleau Pit Water Level = 1305ftRocheleau Pit Water Level = 1305ft

Assume Dew atering to Ele. 1275ft

0.0 58312 f t ³/ sec

0.0

5990

7 ft³

/sec

Distance-400 -300 -200 -100 0 100 200 300 400

Ele

vatio

n (x

100

0)

1.181.201.221.241.261.281.301.321.341.361.381.401.42

16.2 Embankment Stability Evaluation associated with Localized Dewatering If a cut-off system and localized dewatering method were used to construct the proposed roadway embankment, the resulting embankment cross section would be the same as if the embankment was constructed in the dry – after lowering the Rouchleau Pit water level. Therefore, the stability evaluation would be the same as that presented in Section 14.2. 17.0 RISK REGISTRY AND MITIGATION MEASURES BASED ON INSTRUMENTATION MEASUREMENTS/MONITORING OUTCOMES As a part of this project, a risk registry was developed to identify risk issues with the proposed reinforced embankment and the registry includes potential mitigation measures to reduce the risk. A sampling of some of the risks that may result in poor embankment performance of a geosynthetic reinforced embankment constructed over the submerged mine haul road embankment across the Rouchleau Pit include:

1. Poor performance if the construction of the lower 25 ft of the embankment occurs without Rouchleau Mine Pit dewatering.

2. Poor performance of the construction of a 135 ft – 170 ft high geosynthetic reinforced embankment.

3. Poor performance if a Levee or a Geotextile Tube are used to allow dewatering of only the construction zone or only the south end of the Rouchleau Pit.

4. Poor performance associated with the development of 45 and 60 degree embankment side slopes.



5. Poor performance associated with the intensity of Mining Company blasting near the embankment.

6. Risks associated with the construction of a future bridge within the embankment alignment.

7. Poor performance if utility installation occurs within the geosynthetic reinforced embankment.

8. Poor performance resulting from natural occurrences (such as snow, high wind, low temperatures) effecting the construction and performance of the embankment.

9. Poor performance if QA/QC compliance testing is not comprehensive enough during construction.

10. Poor performance if adequate maintenance of the reinforced embankment is not addressed.

The Risk Registry, included in the Appendix, identifies each risk and then includes mitigation measures that can be taken – such as additional testing, additional evaluation and preparing a comprehensive installation and material specification and implementing a comprehensive QA/QC program during construction and a comprehensive instrumentation and monitoring program during construction. Many of the risks and the mitigation measures were evaluated in the Analysis section of this report. The Registry should be considered preliminary; and should continue to be modified and developed during final design development. 18.0 RECOMMENDATIONS FOR PROPOSED CLEAR ZONE FROM TOE OF ROADWAY EMBANKMENT TO OUTSIDE EDGE OF EXISTING MINE HAUL ROAD EMBANKMENT The submerged haul road embankment is bound by steepened mine waste rock fill side slopes on both the north and south sides approximately between roadway stations 6083+00 and 6096+00. At these locations, the submerged embankment crest is approximately 500 ft – 550 ft wide. According to Figure No. 16, the roadway embankment footprint width is anticipated to be approximately 400 – 450 ft where 1H:1V embankment side slopes are proposed and approximately 250 – 300 ft wide where 1H:1.7V embankment side slopes are proposed. A seismic stability analysis for the cross section which included the steepened mine waste rock fill side slopes was performed assuming various “clear” distances between the toe of the proposed E-1A roadway embankment and the edge of the submerged mine haul road crest. The results of the stability analysis, previously shown in Figure No. 24, indicate that a clear zone of 40ft is required to maintain a factor of safety of 1.1 against embankment toe instability during a blasting event that produces a transverse PPA of 0.3g. The 40ft clear zone is shown in Figure No. 29. A 1H:1.7V (60 degree) embankment side slopes is recommended in the area approximately between stations 6089+00 and 6098+50 in order to provide an approximate 40ft clear zone between the toe of the new embankment and the edge of the



existing submerged haul road crest. Other areas through the pit can satisfy the 40ft clear zone with 1H:1V (45 degree) reinforced side slopes. Figure No. 29: 40ft Embankment Clear Between Toe of Reinforced

Embankment and Outside Crest of Submerged Mine Haul Road

19.0 RECOMMENDATIONS FOR DYNAMIC COMPACTION OF EXISTING MINE WASTE ROCK FILL SURFACE

Our review of the IDEA borings drilled into the submerged haul road embankment indicate that the mine waste rock fill may contain more sand size material between individual boulders than in material lower in elevation. Since the upper portion of the mine waste rock fill will be subjected to greater stress increases resulting from the proposed new embankment, this upper zone will be more susceptible to static and dynamic settlement than lower regions of the mine waste rock fill. The variability of the mine waste rock fill is unknown except at a few boring locations. Because of the above factors and the likelihood that the in-place mine waste rock fill gradation and density will vary along the alignment, we recommend dynamic compaction of the in-place ground beneath the embankment footprint and at proposed bridge and abutment foundation locations where foundation support will be on the mine waste rock fill.



Federal Highway Administration Publication No. FHWA-SA-95-037 entitled “Dynamic Compaction” (1995) includes dynamic compaction design guidance. The publication identifies that there have been numerous dynamic compaction projects on mine spoil on transportation projects throughout the country. The author of this publication, Robert G. Lukas-Ground Engineering Consultants, Inc. Northbrook, IL, is a regular team partner with Gale-Tec Engineering, Inc. For mine spoil and landfill deposits, soil and rock mixtures are usually in a medium-dense condition, but often there are pockets of loose material within an otherwise more stable area. Dynamic compaction has been effective in making the subgrade more uniform. Dynamic compaction has also been effective in identifying loose zones of fill. FHWA guidance indicates that Dynamic Compaction is effective in granular/rock spoil as long as the water table is at least 6ft below the surface. Dynamic compaction consists of using a heavy tamper that is repeatedly raised and dropped with a single cable from varying heights by a crane to impact the ground. Tamper weights can range from 10 to 30 tons with drop heights in the range of 30-60 ft above the ground. A grid pattern of drops over the entire footprint area is developed and accomplished in either single or multiple passes. The weight is dropped multiple times on each pass with the number of drops per pass a function of applied energy required and crater depth developed. Following each pass the craters are filled and leveled with a dozer. Dynamic compaction works best on pervious granular deposits where drainage is good and where the water table is at least 6ft below the surface at the time of dynamic compaction. The submerged mine haul road mine waste rock fill appears to meet these requirements. A preliminary dynamic compaction assessment was performed using the following equation:

WHnD = Equation 5 Where: n = an empirical value representative of the soil and groundwater conditions (typically n=0.5) W = the weight of the tamper in metric tons H = the drop height in meters D = the depth of improvement in meters Assuming n = 0.5, assuming the tamper weight equals 20 metric tons and assuming the drop height equals 20 meters, the depth of improvement on this project could approach 10 meters or 33 ft; though large pieces (3 to 5 ft) of mine waste rock fill in the fill matrix could absorb energy and would likely diminish this improvement depth. These preliminary calculations are based on using some of the largest equipment and weights available in the industry. In order to be cost effective, the drop height and weight could be adjusted.



A sufficient amount of energy needs to be applied during dynamic compaction to cause ground compression. The FHWA SA-95-037 guidance suggests a unit applied energy in the range of 600-1100 kJ/m3. Once the tamper weight and drop height are decided upon, the number of drops at each specific drop point location and the number of passes can be determined from Equation 6. AE = (N) (W) (H) (P) Equation 6 (grid spacing)2 Where: AE = applied energy N = number of drops at each specific drop point location W = tamper mass in metric tons H = drop height in meters P = number of passes GS = grid spacing in meters2 Project Specification – Once the final dynamic compaction design is completed, a specification will need to be created that addresses the following issues: • Dynamic compaction footprint • Weight of tamper and drop height for primary and secondary passes, if required • Guidance for cable and hoisting drum • Site preparation • Number of drops per location • Guidance for additional drops depending on crater depth • Monitoring criteria including observations of crater depths, measurements of ground

heave, monitoring vibrations and in-situ testing, to identify improved soil modulus • Placement of additional granular fill required to fill in craters and level the site prior to

construction of the geosynthetic reinforced embankment • Record keeping • Method of measurement and basis for payment

20.0 RECOMMENDATIONS FOR BLASTING CRITERIA/RIGHT OF WAY ACQUISITION NEAR PROPOSED EMBANKMENT

Based on our understanding of the future mining plans in the area, it is likely that UTAC or some other mining company will likely be mining the remaining ore from the Rouchleau Pit and area adjacent to the proposed highway at some point in the future. Based on this assumption, recommendations for limiting seismic forces acting on the proposed E-1A roadway embankment due to future blasting were developed. Seismic forces acting on the proposed embankment can be controlled by varying a parameter known in mining engineering as the scaled distance. The scaled distance uses Charge Weight per Delay of Blasting Material (lbs) and the distance away from the



proposed embankment (Siskind et. al, 1979). The equation, per Siskind, for calculating the scaled distance is given in Equation No. 7.

WDSD = Equation 7

Where: SD = Scaled Distance of Blast Relative to Structure (ft/lbs1/2)

D = Distance from Blast to Structure (ft) W = Charge Weight per Delay of Blasting Material (lbs) A statistical analysis was performed using the Scaled Distance and transverse PPA calculated and measured from each data point presented in the HDR 2012 Blasting Study. The data points are given in Figure No. 30. Normal distributions were generated that estimated the transverse PPA relative to various scaled distances. From this distribution, the probability of a transverse PPA greater than 0.3g, the design value used in the GTE Stability Evaluation, was calculated relative to the scaled distance. The results are given in Table No. 22.

Figure No. 30: Transverse PPA v. Scaled Distance for Blasting Data

Table No. 22: Summary of Scaled Distance Probability Analysis

g = 2 St. Dev. From

Mean g = 3 St. Dev. From

Mean Data Set Average PPA (*g) (95% Less Than) (99.7% Less Than) All Data 0.257 1.79 2.56

Scaled Distance >5.0 0.125 0.43 0.585 Scaled Distance > 10.0 0.114 0.42 0.57



Scaled Distance >13.0 0.084 0.3 0.41 Scaled Distance >22 0.066 0.23 0.3

The results of this analysis indicate that if a blast having a scaled distance of greater than 13 is set off near the proposed roadway embankment, then 95% of the time the transverse PPA will be less than 0.3g. The analysis also indicates that if a blast containing a scaled distance of greater than 22 is set off near the embankment, then 99.7% of the time the transverse PPA will be less than 0.3g. Assuming a change weight of 3000 lbs per delay, a scaled distance of 13 corresponds to a distance of about 700ft from the proposed roadway embankment, while a scaled distance of 22 corresponds to a distance of about 1200ft from the proposed roadway embankment. If the charge can be limited to 3000 lbs/delay and limit the distance of the blast to the embankment toe to no closer than 700ft, then the data suggests that 95% of the time, the PPA will be less than 0.3g and unlikely to exceed the project design requirements.

21.0 RECOMMENDATIONS FOR EMBANKMENT SIDE SLOPE

21.1 Roadway Embankment – Constructed in Dry Conditions The results of the seismic slope stability analysis (0.3g) of the proposed roadway embankment constructed in dry conditions indicate that the governing failure mechanism for the roadway embankment tends to be direct sliding about the base of the embankment at locations along the alignment where the proposed roadway embankment will not be constructed adjacent to the steepened side slopes of the submerged haul road embankment. This occurs approximately from stations 6078+50 (or 6081+00 depending on the bridge cut) to 6089+00 and from 6098+50 to 6101+00 along the proposed roadway alignment where the side slope is 60 degrees. The results of the seismic stability analysis also indicate that an approximately 15% higher factor of safety (1.3 v. 1.15) against direct sliding instability can be obtained if the proposed roadway embankment is constructed with 45 degree side slopes. At locations along the proposed roadway embankment where the embankment will be constructed adjacent to the steepened side slopes, global stability tends to be the governing failure mechanism. This occurs approximately between stations 6089+00 and 6098+50. The results of the seismic stability analysis also indicate that an approximately 10% higher factor of safety (1.2 vs 1.1) against global instability can be obtained if the proposed roadway embankment is constructed with 60 degree side slopes and is thus located a greater distance from the submerged haul road embankment steepened side slopes. Based on these results we recommend that the proposed roadway embankment should be constructed with: • 3H:1V side slopes approximately between Station 6073+50 (where embankment

enters the Rouchleau Pit) to Station 6078+50 (if an MSE is constructed for future



bridge excavation) or Station 6081+00 (to allow for a excavation cut for future bridge installation)

• 1H:1V (45 degree) side slopes approximately between either station 6078+50 or 6081+00 to station 6089+00 and approximately between stations 6098+50 and 6101+00 (where embankment exits Rouchleau Pit)

• 1H:1.7V (60 degree) side slopes approximately between stations 6089+00 to 6098+50 Construction of the embankment with these side slopes at the recommended locations will likely result in factor of safety of at least 1.1 against seismic instability at all stations along the proposed roadway alignment. FHWA recommends a minimum factor of safety of 1.1. 21.2 Roadway Embankment – Lower 30ft Constructed in Wet Conditions The results of the seismic slope stability analysis (0.3g) of the proposed roadway embankment with the base constructed in wet conditions indicate that the governing failure mechanism for the roadway embankment tends to be direct sliding about the base of the embankment through the material placed underwater. This failure mechanism tends to govern regardless of whether the embankment is located adjacent to the submerged haul road embankment steepened sideslopes or not. The failure mechanism factor of safety also does not vary significantly based on the embankment sideslope angle. Based on these results we recommend that if the base of the proposed roadway embankment is constructed in the wet, then it should be constructed with: • 3H:1V side slopes approximately between Station 6073+50 (where embankment

enters the Rouchleau Pit) to Station 6078+50 (if an MSE is constructed for future bridge excavation) or Station 6081+00 (to allow for a excavation cut for future bridge installation)

• 1H:1.7V (60 degree) side slopes approximately between either station 6078+50 or 6081+00 to station 6101+00 (where embankment exits Rouchleau Pit)

Construction of the embankment with these sideslopes at the recommended locations will likely result in factor of safety of at least 1.10 against seismic instability at all stations along the proposed roadway alignment. FHWA-NHI-10-025 recommends a minimum factor of safety of 1.1.

22.0 RECOMMENDATIONS FOR GEOSYNTHETIC REINFORCEMENT

22.1 Material Recommendations Based on the results of this preliminary static and seismic stability analyses we recommend that the primary geosynthetic reinforcement layers have a Design Long Term Reinforcement Nominal Tensile Strength, Tal, as identified Table Nos. 23 and 24.



Table No. 23: Minimum Tal for Primary Geosynthetic Reinforcement for Embankment Construction in the Dry with a Design Seismic Coefficient = 0.3g

Embankment Height (ft) Approximate Geosynthetic

Vertical Spacing (ft) Min. Tal – Machine

Direction (lb/ft) >150ft 3 14,000

100 – 150ft 3 10,300 >150ft 1.5 7,000

100 – 150ft 1.5 7,000

Table No. 24: Minimum Tal for Primary Geosynthetic Reinforcement for Case where Lower 30ft of Embankment is Constructed into Water and Geosynthetic Reinforcement

occurs from 30ft to Top of Embankment, Design Seismic Coefficient = 0.3g

Embankment Height (ft) Approximate Geosynthetic Vertical Spacing (ft)

Min. Tal – Machine Direction (lb/ft)

>150ft 3 14,000 100 – 150ft 3 14,000

>150ft 1.5 7,000 100 – 150ft 1.5 7,000

FHWA-NHI-10-024/025 (Nov. 2009) has a 32 inch maximum vertical geosynthetic reinforcement spacing “consideration for high slopes.” We analyzed 3 ft (36 inch) vertical increments for primary geosynthetic reinforcement. Once the strength of the geosynthetic reinforcement and the facing material for the 60 degree slope are established, the final vertical spacing can be chosen and then analyzed for stability. The vertical spacing and Geosynthetic Tal recommendations provided in Table Nos. 23 and 24 are also based on a specific design seismic coefficient and other factors. We recommend a final stability analysis be performed after all input parameters are selected. The primary geosynthetic reinforcement design strength, Tal, that is specified should be calculated by FHWA-SA-96-071, which calculates the Tal by reducing the ultimate tensile strength of the geosynthetic (ASTM D6637 for geogrids and ASTM D4595 for geotextiles) in the machine roll direction by applying a series of reduction factors for creep, durability and installation damage. Values for these reduction factors are product specific and must be represented by testing submitted by the Manufacturer. For this project, we recommend product/project specific testing for installation damage. Installation damage of the geosynthetic is a concern as the result of the potential larger pieces of rock particles that may be allowed in the reinforced embankment fill. As such, we recommend that a field installation damage testing program be designed and implemented using the proposed reinforced embankment fill and a uniaxial strength geogrid and/or a uniaxial high strength geotextile in order to establish a installation damage factor.



A relatively high interaction coefficient between the primary geosynthetic reinforcement material and the embankment fill of approximately 85% of the embankment fill material angle of internal friction was considered for our analysis. Geogrids, with their inherent openings for aggregate interlock, and high strength geotextiles, with rough surface textures, can develop the required interface friction. Product/project specific testing should be performed to determine this value for the selected primary geosynthetic and the selected reinforced embankment fill. 22.2 Placement Recommendations

Based on the results of the static and seismic stability analyses, we recommend the following vertical increments and horizontal lengths for the primary geosynthetic reinforcement of a back-to-back embankment:

• At locations where the embankment height is less than 100 ft, the primary geosynthetic reinforcement should be placed at a maximum of 32 to 36 inch vertical increments at lengths as determined from the Stability Analysis or at least equal to 100% of the embankment height at that location for both 1H:1V (45 degree) and 1H:1.7V (60 degree) embankment side slopes.

• At locations where the embankment height is greater than 100 ft, the primary geosynthetic reinforcement should be placed at a maximum of 32-36 inch vertical increments at lengths as determined from the Stability Analysis or at least equal to 115% of the embankment height at that location for 1H:1V embankment side slopes.

• At locations where the embankment height is greater than 100 ft, the primary

geosynthetic reinforcement should be placed at a maximum of 32-36 inch vertical increments at lengths as determined from the Stability Analysis or at least equal to 110% of the embankment height at that location for 1H:1.7V embankment side slopes.

• At locations where one side slope is shorter than the other, due to existing grade differences at the base of the embankment, the primary geosynthetic reinforcement length should be calculated based on the slope height for the side being reinforced.

Due to the nature of a back-to-back geosynthetic reinforced embankment, the horizontal primary geosynthetic layers have to be staggered from one side slope relative to the other so that they do not intersect at the same elevation in the center of the embankment. We recommend that the geosynthetic reinforcement elevations be staggered such that there is at least 1 ft of separation between layers. We recommend that reinforced embankment fill be compacted in maximum 12 inch loose vertical lifts, except for the upper 5 ft of the embankment which should be compacted in



maximum 9 inch loose vertical lifts. The 12 inch loose lift satisfies MnDOT 2105 and FHWA guidance. For the 1H:1V side slopes, where the primary geosynthetic reinforcement may be between 1.5 and 3 ft vertical increments, we recommend secondary geosynthetic reinforcement be placed at the slope face for every 12 inch lift of fill. Secondary reinforcement could consist of a polyester geogrid or a polypropylene/polyester mesh placed with a Tal of 400 lb/ft in the direction placed. The material should extend from the slope face (extending through any topsoil placement to the slope face) to at least 6 ft back into the reinforced embankment fill. For the 1H:1.7V (60 degree) slope face, a construction form and/or permanent facing element such as a galvanized welded wire basket, HDPE cellular confinement web, gabion or some other acceptable facing element should be used at the face. For example, if a L-shaped 18 inch x 18 inch welded wire basket is chosen as the face of a 60 degree side slope and a 3ft vertical primary geosynthetic reinforcement spacing is selected, then a primary geosynthetic layer would exist for every two baskets. The primary geosynthetic should be wrapped around the face and then back at least 4ft. Secondary reinforcement, placed at every other basket should have a Tal of 400 lb/ft. The secondary geosynthetic reinforcement should be placed with a 6ft horizontal length in addition to wrapping around the face and a 4ft wrap back. The RSS slopes for the geosynthetic reinforced embankment for this project cannot be designed using the MnDOT RSS design template. Given the overall embankment height, as well as the seismic considerations, the MnDOT RSS template does not apply to the design of this embankment. A project specific design should be required.

23.0 RECOMMENDATIONS FOR 1H:1V AND 1H:1.7V EMBANKMENT SLOPE FACING

The E1-A embankment across the Rouchleau Pit is proposed to have 1H:1V (45 degree) and 1H:1.7V (60 degree) side slopes. Both of these slope angles have been constructed with vegetated faces on State and State-Aid projects throughout Minnesota and Country-wide. 1H:1V Geosynthetic Reinforced Slopes are common throughout Minnesota and Country-wide. In Minnesota, most, if not all of these slopes are vegetated. The largest RSS in the Country, 242ft in height, constructed at Yaeger Airport in West Virginia is also vegetated. We recommend a 6 inch minimum Premium Topsoil layer (possibly supplemented with compost and/or mixed with gravel) be placed at the slope face. The primary and secondary geosynthetic reinforcement should extend through the topsoil to the slope face. Wrapping of the face is not required for a 1H:1V slope per FHWA-NHI-10-025. Seed, slow release fertilizer and a synthetic erosion control blanket that is pinned and/or keyed into the slope should make up the face. The slope should be vegetated and protected with the erosion blanket in no more than 12ft vertical construction increments.



The 1H:1.7V (60 degree) slope face can be constructed with various vegetated and/or gabion facings. One common 60 degree vegetated slope facing for Minnesota DOT and Minnesota State-Aid projects include a geogrid wrap of a galvanized welded wire basket face form and with a synthetic erosion mat wrapping the face inside of the geogrid. Alternately, the secondary reinforcement can be a mesh type material (Miramesh® is one brand) that could serve the purpose of both secondary reinforcement and maintaining the soil at the face. Whichever product is specified, an Ultraviolet Light (UV) inhibitor should also be specified. For this facing system, six (6) inches minimum of Premium Topsoil and/or compost and/or gravel should be placed at the face and seeded and fertilized in no more than 12ft vertical construction increments. A Biotic Earth® type product could also be hydromulched into the slope face. The wire baskets could be 10ft long x 1½ft high x 1½ft wide in dimension and consist of galvanized 4 inch by 4 inch W4.0 x W4.0 wire conforming to MnDOT Spec 3303 and 3393 and held in place with tensioned galvanized struts. Galvanizing by the hot-dipped or Galfan system can be considered. Alternative facing materials could include a cellular confinement web type product (HDPE honeycombed web) with the outer two cells infilled with a topsoil or a Gabion-Rock type system.

24.0 RECOMMENDATIONS FOR PREQUALIFICATION EMBANKMENT FILL MATERIAL TESTING

We recommend the glacial till, the mine waste rock fill that is stockpiled on-site, and crushed bedrock that will be cut from the east and west sides of the Rouchleau mine pit be considered as reinforced embankment fill material. The material will likely need to be crushed and/or screened to obtain a gradation appropriate to use with geogrid reinforcement. Our analysis (Report Section 14.0) was performed considering a reinforced embankment fill with a wet unit weight of 125 pcf which would be a typical value for a screened glacial till. Crushed rock fill would be heavier and if considered as reinforced embankment fill, would require stability to be re-analyzed with new input values.

We recommend a testing program be implemented in order to assess a cost effective gradation based on on-site crushing of the excavated on-site soils. Full scale installation damage laboratory testing per ASTM D-5818 and interface friction testing is recommended for the primary geosynthetic reinforcement and potential reinforced embankment fill soils. The final embankment design should be based on the results of this program.



At this time, we recommend that the reinforced embankment material conform to the following minimum properties:

• Angle of Internal Friction per ASTM D3080 (Direct Shear Test) of 35 degrees for material compacted to 95% to 98% of the AASHTO T99 maximum dry density at +/- 1% of Optimum Moisture Content (Large Box testing is recommended considering the potential for larger rock pieces in the fill)

• Percent Passing the U.S. No. 200 Sieve no more than 12% by dry weight • Maximum Particle Size of 3 – 4 inches • pH between 5 and 10

If a reinforced embankment fill with greater than 12% fines is chosen, then approximate 3 ft. thick drainage layers consisting of free draining gravel such as No. 57 stone should be extended continuously from one side of the embankment to the other side. These layers should be included every 25 – 50ft vertical. If a portion of the embankment is to be constructed into standing water, then a prequalification testing program similar to that identified above, should also be performed for this material. The portion of the roadway embankment constructed with 3H:1V embankment side slopes to facilitate future bridge installation, approximately between station 6073+50 and 6078+50, or 6081+00 depending on the bridge cut, will not need to be constructed with material meeting the above requirements. This portion of the embankment could be constructed with a Granular Borrow or potentially a Common Borrow material modified such that the angle of internal friction meets the strength requirements determined from a seismic stability analysis. 25.0 RECOMMENDATIONS FOR EMBANKMENT FILL TESTING DURING

CONSTRUCTION We anticipate that the glacial till material available in the cut areas for this project may be highly variable with regard to gradation, fines content and maximum particle size. Thus, even with a mechanical crushing/washing and potentially blending prior to fill placement the material is likely to contain some variability with regard to density and strength as represented by the angle of internal friction. The density and angle of internal friction of the reinforced embankment fill material are two of the more important parameters with regard to the stability of the reinforced embankment. Additionally, the Monte Carlo simulations show that variability in the embankment fill friction angle could effect slope stability. Therefore, we recommend an on-site testing program be implemented for the embankment fill material. We recommend that gradation (AASHTO T-27), standard Proctor Dry Density (AASHTO T-99 or ASTM D698) and Direct Shear (AASHTO T-236 or ASTM D3080) laboratory testing be performed at regular intervals on the underwater fill and/or the



reinforced embankment fill material. The project specifications should include minimum standards for these laboratory tests in additional to field compaction testing.

26.0 RECOMMENDATIONS FOR UTILITY INSTALLATION IN REINFORCED EMBANKMENT

Storm, sanitary, water and various other utilities are proposed to be placed within the upper portion of the reinforced granular embankment. A leaking water main, storm or sanitary sewer could result in saturated soil and potential side slope instability. Additionally, cutting the geosynthetic reinforcement to maintain a buried utility can compromise the integrity of the embankment. FHWA guidance (FHWA-NHI-10-024) - “Design and Construction of MSE Walls and RSS”, 2009) states that utilities in the reinforced soil mass should be avoided and if avoidance is not possible, “utilities should only be placed in double wall design systems such as locating utilities inside box culverts with inspection galleries or using double wall pipe with instrumentation to indicate leakage. Only leak proof joints should be used on drainage pipes.” 26.1 Encapsulation of Utilities within Concrete Box Culvert or Two Retaining Structures. We recommend that the utilities be installed within the embankment such that they can be accessed without reinforced embankment excavation and such that the reinforced fill is protected in the event of a utility leak or break. Some options include installation of the utilities within a concrete box culvert with inspection galleries located near the edge of the Mesabi Trail side of the embankment and/or installation of utilities between a gravity retaining wall structure (such as a wet cast Big Block similar to ReCon or LondonStone) on the outside edge of the embankment and a MSE structure on the inside – with the geosynthetic reinforcing the MSE interior wall extending below the pavement - such that geosynthetic reinforcement for the embankment side slope would not be required on the Mesabi Trail (Utility Corridor) side of the embankment. If this was chosen as the design, double lined pipes, to reduce the potential for leaks, would be recommended. These options are illustrated in Figure Nos. 31 and 32.



Figure No. 31: Box Culvert Containing Utilities within Reinforced Embankment

Figure No. 32: Utility Conduit within Reinforced Embankment Constructed with MSE and Big Block Wall Faces

26.2 Geosynthetic Diversion Around Utilities not Encapsulated in a Box Culvert or between Two Retaining Walls Some utility lines that may not be encapsulated in a box culvert or between retaining walls and which run horizontally through the reinforced fill will require the geosynthetic reinforcement that intercepts the utility pipes to have to be diverted around them. This diversion can occur by inclining or declining the geosynthetic at angle of no more than 10 degrees from horizontal to facilitate utility installation. At least 2 inches of fill material should be placed between any utility and the geosynthetic reinforcement. Figure No. 33 shows a typical detail for geosynthetic diversion around utility lines. If this type of system was implemented, the utilities should be a double-walled pipe and would need to be installed concurrently with reinforced embankment construction.

Geosynthetic Reinforcement

Geosynthetic Reinforcement

Retaining Wall with Modular Block or Welded Wire Facing

Big Block Gravity



Figure No. 33: Geosynthetic Reinforcement Diversion around Horizontal Utility Lines

27.0 RECOMMENDATIONS FOR ROUCHLEAU PIT DEWATERING FOR EMBANKMENT CONSTRUCTION

The water level in the Rouchleau Mine Pit was reported at an elevation of approximately 1305ft, in August, 2013. The MnDOT bathymetric survey indicates that the crest of submerged haul road embankment is at an elevation ranging from 1285 – 1280 ft. In order to perform dynamic compaction of the mine waste rock foundation material and construct the lower portion of the reinforced E-1A roadway embankment in the dry, lowering of the Rouchleau Pit water level will be required. FHWA guidance suggests that for dynamic compaction operations, the groundwater table should be lowered to a depth of approximately 6 ft below the ground surface, or an elevation of 1274 ft during this portion of the work. The water level in the pit will need to remain at an elevation of 1274 ft during dynamic compaction and for the initial portion of embankment construction. Once embankment construction has reached an elevation of 1315 – 1305 ft, then the pit water level can be raised. We recommended maintaining at least a 10 ft difference between embankment crest elevation during construction and the pit water level.

28.0 RECOMMENDATIONS FOR EMBANKMENT MONITORING DURING/POST CONSTRUCTION

We recommend that at least 3 to 5 stations be selected for instrumentation installation and monitoring. Embankment Settlement Monitoring The results of the marine resistivity study, the subsurface exploration and the settlement analysis presented in Section 14.1 indicate that there is likely variability in the properties and thickness of the mine waste rock fill material. Several feet of settlement and up to 1ft - 2ft of differential settlement along the embankment alignment is likely. We recommend that besides the 3 to 5 instrumentation stations that will be monitored, that settlement plates be installed at the slope top crest, outside the limits of the pavement, at least every 200 ft to monitor for settlement after construction. Settlement monitoring should continue for at least a year post after embankment construction is complete.

Geosynthetic reinforcement wrapped over and under proposed utilities pipes with 2 inch min. backfill cushion

Insulated Utility pipes shall be installed concurrently with RSS Construction – at least 8ft horizontal away from the face an no more than 6ft vertical from the surface



Embankment Stability Monitoring Slope deformation is possible depending on the nature of the mine waste rock fill embankment foundation soils and based on the geosynthetic interaction with the embankment fill. Slope inclinometers are recommended at the top outside crest of both sides of the embankment, on the midbench and at the toe of both sides of the embankment at each monitoring station. Slope inclinometer casing is planned to be installed in select boreholes in conjunction with IDEA Drilling, Inc. work off a barge in Spring, 2014. These casings should be extended up through the reinforced embankment fill during construction; and continued to be monitored. Embankment Strain Monitoring Strain monitoring is proposed at locations where FLAC-Slope modeling indicated strain development would occur. A combination of the following three (3) types or strain monitoring should be used. SR-4 type strain gages, fiber optic strips, such as Geodetect® and rod extensometers. The gages should be installed in horizontal lines extending from beneath the slope crest to the embankment slope face. Gages at 3 to 5 levels at each station should be considered. One set of gages should be installed within 5 ft. of the surface of the submerged mine haul road crest (elevation 1280-1285 ft) at each monitoring station. The next set of gages could be located just above the existing water level (elevation 1305 ft) to reduce wiring and waterproofing requirements of some of the instrument types. Strain gage types such as SR-4 strain gages could be pre-attached to the geosynthetic either at the manufacturing facility or at a warehouse near the site, to reduce interference with construction. Embankment Pore Water Pressure Monitoring Excess pore water pressure build-up during and after embankment construction could result in embankment instability. Vibrating Wire Pore Pressure Cells should be installed at the temporary dewatered elevation (elevation 1274 ft), midpoint between the temporary dewatered elevation and the existing water elevation of 1305 ft (elevation 1390 ft) and at the long term water table elevation (to be determined) within the embankment at each monitoring station. Embankment Blast Monitoring Post construction embankment monitoring should include at least two (2) seismograph recording stations to monitor vibrations from future seismic events. Accelerometers are planned to be installed in several of the borings in conjunction with IDEA Drilling, Inc. work off a barge in the Spring, 2014. These units should be monitored long-term. Ralph B. Peck Observational Method We recommend that the Peck Observation Method be used during construction. This method was developed for complex projects by Dr. Karl Terzaghi and Dr. Ralph Peck in the last century. Dr. Peck provided a review of the method in a 1969 paper (Rankine Lecture) for “Geotechnique”.



The method includes in part:

• Perform general subsurface exploration but not necessarily in detail,

• Assess and analyze favorable and unfavorable conditions,

• Monitor performance,

• Have a course of action selected in advance for unfavorable conditions and

Modify design to suit actual performance.

29.0 RECOMMENDATIONS FOR FURTHER TESTING AND EVALUATION We recommend further testing of the following embankment fill soils and the in-place mine waste rock fill prior to final design:

• Cross Hole Seismic Testing (ASTM D-4428) of the in-place mine waste rock fill at locations where anomalies were detected by marine resistivity (This work is planned to be performed in conjunction with IDEA Drilling, Inc. work off a barge in the Spring, 2014)

• Laboratory Gradation (ASTM D-4223) and Compacted Shear Strength-Angle of Internal Friction (ASTM D-3080) Study of proposed reinforced embankment fill blends and proposed underwater aggregate fill blends, if used, to optimize the properties,

• Slug and/or Pump Tests of the in-place mine waste rock fill (ASTM D-4044) and

• Installation Damage (ASTM D5818) and Pullout (ASTM D6706) testing of the selected primary geosynthetic reinforcement type with the various blends of reinforced embankment fill material

Based on the results of the borings and electrical resistivity, we recommend that Cross Hole Seismic be performed at the following locations along the proposed roadway embankment: Proposed Roadway Embankment Stations Location 6095+00 South side of Embankment near toe of Proposed Roadway Embankment 6095+00 Same as Above, but near Crest of Submerged Haul Road Embankment Sideslopes (near Boring No. 31069) 6092+00 Crest of Submerged Haul Road Embankment Sideslope, South side of



Proposed Roadway Embankment 6090+00 Crest of Submerged Haul Road Embankment Sideslope, North side of Proposed Roadway Embankment We recommend further evaluation of the following issues prior to/during final design:

• Evaluate the stability and distortion effect of mining company blasting on the embankment by finite element methods (Quake-W, FLAC or other),

• Use result of this analysis to determine final seismic coefficient to be used for embankment design,

• Evaluate potential long term Rouchleau Pit high water level • Analyze underseepage into the construction zone for the rock/till levee or

geotextile tube approach after the slug test results become available, • Analyze the Cross Hole Seismic Test results and compare them to the

assumptions made in the analysis and • Perform limit equilibrium analysis of final soil and embankment geometry

with selected geosynthetic allowable design load.

30.0 RECOMMENDATIONS FOR FUTURE BRIDGE ALONG ALIGNMENT

30.1 Future Bridge Installation MnDOT is considering including an un-reinforced section along the alignment as a location where a future bridge would be installed so that mining equipment can access beneath the roadway. The bridge will be placed approximately between stations 6074+27 and 6078+32 along the roadway alignment. This is located on the east side of the existing pit, approximately where the roadway alignment first enters the Rouchleau Pit. The bridge is required to have an 80ft clear span to allow mining equipment to pass beneath it. The location of the bridge is given in Figure No. 35. 30.2 Embankment Section to Facilitate Future Bridge Installation The proposed roadway embankment at the future bridge is proposed to be constructed with 3H:1V side slopes, without geosynthetic reinforcement, so that the future bridge foundation installation would not have to excavate into the geosynthetic reinforcement, which could potentially cause embankment instability. The proposed roadway profile from Stations 6070+00 to 6078+50 shows that the embankment height in this area varies from 60ft at the eastern portion to 160ft at the western portion. Given the embankment height and crest width, the unreinforced embankment width will be approximately 1140ft at the western portion of the proposed bridge section.



The length of the unreinforced section will need to take into account the cut that will need to be made on both sides of the unreinforced embankment to facilitate bridge foundation installation and abutment construction. We anticipate the cut slopes into the unreinforced embankment will be approximately 1.5H:1V, and given a 160ft fill height, will add an extra 250ft of unreinforced section on the west side of the proposed bridge. On the east side of the proposed bridge, the unreinforced section should extend to the existing Rouchleau Pit highwall at approximately stations 6073+50. On the west side, taking into account the additional cut, the unreinforced embankment should extend to station 6081+00. The bridge location relative to the embankment profile is shown in Figure No. 34.

Figure No. 34: Future Bridge Location along Proposed Alignment

Near the western portion of the unreinforced section, near station 6081+00, an approximately 50ft transition zone shall be included to transfer the side slope angle from 3H:1V to 1H:1V. Geosynthetic reinforcement should be included within the embankment at locations where the embankment side slopes are at a 2H:1V or steeper angle. 30.3 MSE Wall Construction to Facilitate Future Bridge Installation Between approximate stations 6078+50 and 6081+00, the embankment will be approximately 150 – 170ft high. Un-reinforced 3H:1V side slopes are proposed to facilitate a cut to be made for future bridge installation. One method for reducing the 3H:1V embankment section would be to construct a geotextile wrapped face MSE wall at a 70 degree (or steeper) angle near the proposed bridge abutment at approximately Station 6078+32. This MSE wall would replace the 1.5H:1V cut slope, which would allow for the tall embankment sections between stations 6078+50 and 6081+00 to be constructed with 1H:1V (45 degree) side slopes. We estimate that MSE wall construction

1.5H:1V Cut Slope for Bridge Foundation Installation

Sta 6074+50 Sta 6078+50



at the future bridge abutment location will eliminate approximately 0.5 million in-place CY of fill material now, and would save a significant amount of fill from being excavated in the future. A wrapped face MSE could vary in height from approximately 60ft - 150ft depending on the location and slope angle chosen for the MSE wall. The MSE wall would be constructed concurrently with the rest of the reinforced embankment. The geosynthetic reinforcement would run parallel to the centerline of the embankment and would have to be placed at an offset elevation to the geosynthetic reinforcement supporting the roadway embankment side slopes. We recommend at least a 0.5ft vertical offset between layers of geogrid reinforcement. The MSE wall would be buried by the un-reinforced embankment section during initial embankment construction and could then be exposed during excavation for the future bridge. The MSE wall would need to be designed once the final geometrics are chosen. 30.4 Recommendations for Future Mine Access Bridge Foundation MnDOT is considering a three span mining access bridge for future installation. The bridge foundations are planned to be located on a shelf on the east side of the Rouchleau pit approximately between stations 6074+27 and 6078+32. MnDOT is considering spread footings for the bridge abutment foundation and piling for the bridge pier foundation. According to borings 31072 and 31073, the soil conditions at the locations of potential bridge abutments consist of approximately 70 - 120ft of mine waste rock fill over bedrock which may make pile installation to bedrock difficult. Possible bridge foundation alternatives include a shallow spread footing bearing on the mine waste rock fill, piles end bearing in the mine waste rock fill, piles end bearing on bedrock and drilled shafts socketed into bedrock. Spread Footing Foundation System -Shallow spread footings could be used as the foundation system for the bridge abutment. The shallow spread footings would bear on the mine waste rock fill. It is likely that the bearing capacity of a spread footing foundation system will be governed by the settlement potential of the mine waste rock fill material. A settlement analysis of the spread footing foundation system on mine waste rock material was performed to determine the potential bearing capacity of a shallow spread footing. The analysis was performed assuming a tolerable settlement of 1 inch and that the spread footing length at the abutments would be at least the width of the proposed TH 53 roadway, which is 125ft at the abutment locations. Though the proposed abutment loads have not been determined, we recommend the abutment spread footings associated with the bridge abutments placed on the mine waste rock fill be designed for a net allowable bearing pressure of 4000 psf. Assuming this bearing stress and assuming the settlement properties of the mine waste rock fill based on



our literature review, a spread footing at the bridge abutments with a length of 125ft and a width of 10ft could result in less than 1 inch of abutment settlement. If the footing width was increased to 15ft then settlement could be less than ½ inch. These settlement estimates are based on the empirical settlement properties estimated for the mine waste rock fill. The settlement analysis also assumes that the rock fill is relatively homogeneous, which is likely not the case due to the range in particle size and nature of deposition. Preloading of footings bearing on mine waste rock fill, in conjunction with load testing/settlement monitoring, could be performed. We recommend the over excavation of the mine waste rock fill to a depth of 3ft beneath the concrete spread footing and the replacement with a compacted Aggregate Bedding, MnDOT Spec 3149.2F. The width of the aggregate bedding layer should be approximately 5ft wider than the width of the footing directly beneath the footing and should extend out at an angle no steeper than 1H:1V to a depth of 3ft below the bottom of the spread footing. Drilled Shaft Foundation System- Bridge pier and Abutment foundations could include drilled shafts extending through the mine waste rock fill and socketed into bedrock. Drilled shafts could be drilled with Specialty equipment utilizing cluster drills with carbide or diamond teeth. The casing used to support the sides of the shaft (75 to 120 ksi yield strength) would likely remain in-place and the shaft filled with an 8000 psi compressive strength concrete and reinforced with a rebar cage. Driven Pile Foundation System - A hybrid method for conventional CIP pipe pile installation through the mine waste rock fill could be to use a down-hole driving (DHD) hammer with a Superjaws® overburden drill bit, manufactured by Numa Hammers® to predrill and set CIP pipe piling into bedrock. The Superjaws bit system and DHD hammer is specially designed for CIP Pipe pile in boulder fill. This hybrid system uses both a downhole hammer for driving and a rotating Superjaws bit for augering or “predrilling” to advance the casing/pile. The individual bits are slightly larger than the diameter of the casing and predrill a borehole for pile installation by cutting/displacing boulders while drilling. Once the desired depth has been reached, then the Superjaws® bit is retracted up through the casing and the pile is set. Case studies provided by Numa indicate that this system can be used to install pipe piles through boulders or rock fill. A local Contractor reports the use of this system approximately a half-dozen times in Minnesota, and indicates a practical pile penetration depth through rock fill of 50ft. If this type of pile installation system is to be considered, we recommend a test pile program prior to pile installation. We recommend, depending on the load capacity requirements, 12 inch or 16 inch CIP pipe piles extending through the mine waste rock fill into bedrock. Pile capacity from installation into bedrock will likely be governed by the allowable structural pile capacity. According to the 2013 subsurface exploration, the bedrock at the bridge pier locations is likely to consist of intact, high strength Cherty bedrock from the Biwabik Iron Formation. Bedrock was encountered at an approximate elevation of 1270 - 1240ft.



31.0 PRELIMINARY REINFORCED EMBANKMENT FILL/GEOSYNTHETIC QUANTITIES Preliminary plan quantities of materials were estimated based on the average height of the embankment at 50 ft intervals along the portion of the E-1A alignment between stations 6073+50 and 6101+00. Similar to the embankment footprint widths, the preliminary quantities calculated are based on the elevation of the centerline and do not take into account any variability of the ground surface at the station offsets. Preliminary quantity estimates are included for that portion of the proposed embankment from Station 6073+50 to 6078+50 at 3H:1V side slopes, from Station 6078+50 to 6089+00 and from Station 6098+50 to 6101+00 at 1H:1V side slopes and from Station 6089+00 to 6098+50 at 1H:1.7V side slopes. A preliminary quantity estimate for the primary and secondary geosynthetic reinforcement was obtained by estimating the required layers of reinforcement and the length of the reinforcement at 50 ft intervals along the proposed embankment alignment. The estimated reinforcement quantity is based on the centerline height of the embankment and does not account for any variability in the grade of the existing ground surface at station offsets. The preliminary plan quantity is for a back to back RSS embankment constructed in the dry, at the slope angles and stationing as included above. For the preliminary quantity estimate we assumed primary geosynthetic reinforcement placed at a 3ft vertical spacing. We assumed secondary geosynthetic reinforcement placed between layers of primary geosynthetic reinforcement at a 1ft vertical spacing within the 1H:1V side slope embankment and between primary geosynthetic reinforcement at a 1.5 ft vertical spacing within the 1H:1.7V side slope embankment. Our preliminary quantity estimate is: • The dynamic compaction of 105,000 square yards (2300 lineal ft x 400 ft wide) of

surface material, • The screening and/or crushing and placement of about 2.9 million cubic yards plus

settlement compensation of about 186,000 cubic yards of reinforced granular embankment fill material for the 1H:1V and 1H:1.7V embankment side slopes (from Station 6078+50 to Station 6101+00),

• The placement of about 3.8 million square yards of primary geosynthetic reinforcement if placed in 3.0ft vertical increments and 1.0 million square yards of secondary geosynthetic reinforcement, both ,

• The placement of about 0.7 million square yards of Common or Granular Borrow for the 3H:1V side slope embankment between Station 6073+50 to 6078+50.

This quantity does not include waste and overlap.



32.0 GENERAL QUALIFICATIONS

This report has been prepared in order to aid in the preliminary design of T.H. 53 E-1A Embankment Relocation. The scope is limited to the specific project and location described herein, and our description of the project represents our understanding of the significant aspects relevant to soil and foundation characteristics. In the event that any changes in the design, as outlined in this report, are planned, we should be informed so that changes can be reviewed and the conclusion of this report modified or approved in writing. As a check, we recommend that we be authorized to review preliminary design concepts and reports and final design to confirm that our report recommendations have been interpreted in accordance with our intent. Without this review, we will not be responsible for misinterpretations of our data, or analysis and/or our recommendations nor how these are incorporated into the final design. The analysis and recommendations are based on the data obtained from soil and rock borings performed at the locations indicated in this report and other site information provided to us. This report does not reflect any variations which may occur between borings or any variations from site information provided to us. In the performance of subsurface explorations, specific information is obtained at specific locations and at specific times. It is a well-known fact that variations in fill condition, and in soil and rock conditions occur at most sites. The nature and extent of the variation may not become evident until the course of construction. If variations appear during construction, it will be necessary for a re-evaluation of the recommendations of this report after performing on-site observations during the construction period and noting the characteristics of any variations.

APPENDIX

1. Boring Location Diagram 2. Boring Drill Logs 3. MnDOT Underground Mine Map 4. MnDOT Geophysical Testing Results 5. Embankment Settlement Analysis Sample Calculation 6. Embankment Stability Analysis Results 7. Risk Registry 8. Case Histories of Similar Projects 9. References

minnesota department of · pdf file19.0 recommendations for dynamic compaction of ... figure...

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