geotechnical engineering report wintercrest lane & arundel
TRANSCRIPT
GEOTECHNICAL ENGINEERING REPORT
Wintercrest Lane & Arundel Drive Storm Water Improvements
Charlotte, North Carolina
Prepared For:
7500 East Independence Blvd
Suite 100
Charlotte, NC 28227
Prepared By:
4107-F Rose Lake Drive
Charlotte, NC 28217
Project No. 100-19-058
December 13, 2019
1
December 13, 2019
David Bocker, P.E.
NV5
7500 East Independence Blvd, Suite 100
Charlotte, NC 28227
Reference: Subsurface Exploration and Geotechnical Analysis
Wintercrest Lane & Arundel Drive Storm Water Improvements
Charlotte, Mecklenburg County, North Carolina
Dear Mr. Bocker:
Capstone Civil Engineering, Inc. (CCE) has completed the subsurface exploration and geotechnical
analysis for the above referenced project in Charlotte, NC. This report contains a brief description
of the project information provided to us, general description of the site subsurface soil conditions
encountered during our subsurface exploration, and our geotechnical design recommendations for
the replacement of the existing storm water pipe.
We are available to review with you the recommendations presented herein and answer questions
you may have. We have enjoyed working with you and look forward to our continued
association as your geotechnical consultant on the remainder of this project and any future projects
you may have.
Should you have any questions regarding this report or if we may be of further assistance, please
feel free to contact us at your convenience.
Respectfully,
CAPSTONE CIVIL ENGINEERING, INC.
Cirilo Saba, MCE
Staff Professional
Charles M. Brown, P.E.
Principal Engineer
12-13-19
2
REPORT OF PRELIMINARY SUBSURFACE EXPLORATION
AND GEOTECHNICAL ANALYSIS
WINTERCREST LANE STORM WATER IMPROVEMENTS
CHARLOTTE, MECKLENBURG COUNTY, NORTH CAROLINA
TABLE OF CONTENTS
EXECUTIVE SUMMARY .............................................................................................................................. 3
1.0 SCOPE OF EXPLORATION ........................................................................................................................... 3
1.1 Field Exploration ...................................................................................................................................... 4
1.2 Laboratory Services .................................................................................................................................. 4
2.0 PROJECT INFORMATION ............................................................................................................................ 4
2.1 Project Information ................................................................................................................................... 4
2.2 Site Location and Description .................................................................................................................. 4
3.0 SUBSURFACE CONDITIONS ....................................................................................................................... 4
3.1 Regional Geology ..................................................................................................................................... 4
3.2 Field Exploration ...................................................................................................................................... 5
3.3 Surface.. ..................................................................................................................................................... 5
3.4 Subsurface ................................................................................................................................................. 5
3.5 Fill Soil. ................................................................................................................................................. …5
3.6 Residual Soil ............................................................................................................................................. 5
3.7 Partially Weathered Rock ......................................................................................................................... 5
3.8 Auger Refusal ........................................................................................................................................... 6
3.9 Groundwater Observations ....................................................................................................................... 6
3.10 Laboratory Testing .................................................................................................................................... 6
4.0 PROJECT DESIGN AND CONSTRUCTION RECOMMENDATIONS ..................................................... 6
4.1 Site Preparation ......................................................................................................................................... 6
4.2 Excavation ................................................................................................................................................. 6
4.3 Fill Material and Placement ...................................................................................................................... 6
4.4 Cut and Fill Slopes…………. .................................................................................................................. 7
4.5 Plans and Specifications Review .............................................................................................................. 7
4.6 Fill Construction Observation and Testing .............................................................................................. 7
5.0 CONCLUSION……… ..................................................................................................................................... 7
APPENDICES
APPENDIX A - Figures
Figure 1 - Site Vicinity Map
Figure 2 - Boring Plan
APPENDIX B - Boring Logs
APPENDIX C - Laboratory Testing Results
APPENDIX D - Supplemental Information
3
EXECUTIVE SUMMARY
This executive summary provides our understanding of the project and an overview of our
findings and recommendations. Data and recommendations given herein should not be used
without review of the entire report. These recommendations are based on three (3) soil borings, as
shown on the boring map as B-1, B-2, and B3, performed on site by a drill rig and crew to depths
of 20 feet.
The project site is comprised of an existing storm water pipe located along Wintercrest Lane
and Arundel Drive in Charlotte, North Carolina. Figure1 in the appendix presents the
approximate site location and vicinity.
Based on the information provided to our office by NV5 Engineers, it is our understanding that
the existing 24”/30”36” RCP along Wintercrest Lane and Arundel Drive will be replaced with
a 8’x3’precast box culvert, as a part of the various storm drainage improvement projects.
Capstone Civil Engineering (CCE) has been tasked to determine the general subsurface
conditions, the likelihood of encountering rock while replacing the pipe, and obtain the
necessary geotechnical information for design purposes. Three (3) soil boring tests (SBT)
were proposed for this project. See attachments for proposed boring locations. The borings
extended to depths of 20 feet below the existing surface, or at auger refusal in competent
rock.
Subsurface conditions at the site, as indicated by the borings, generally consist of 4 inches of asphalt,
underlain by fill material made mainly of, SILTS, CLAYS, and SANDS, underlain by residual
CLAYS and SANDS, underlain by partially weathered rock (PWR) and underlain by material hard
enough for auger refusal to depths of approximately 16 to 19.5 feet below the existing ground surface
elevation. Blow counts from the Standard Penetration Test (SPT) yielded N-values that ranged
from 0 to 50/1” blows per foot (bpf) to the depths explored.
Based on the results of our subsurface exploration and our understanding of the proposed
construction, the presence of bedrock and groundwater is likely to be encountered during
construction. Groundwater was encountered during our exploration at two (2) of the boring
locations, to the depths explored as shown on the associated boring logs. Subsurface conditions in
short distances from the boring performed onsite should be consistent with our findings but are not
guaranteed.
1.0 SCOPE OF EXPLORATION
1.1 Field Exploration: The preliminary subsurface exploration included the execution of three (3)
soil test borings designated B-1, B-2, and B-3, performed at the approximate locations shown on the
Boring Location Diagram (Figure 2) included in the Appendix. The boring locations were established
by NV5 and located in the field by CCE. personnel. The borings were extended to depths of 19.5
feet below the existing ground surface using continuous-flight, hollow-stem augers.
Standard Penetration Tests were performed in the borings at designated intervals in general
accordance with ASTM D 1586-84. The standard penetration test is used to provide an index for
estimating soil strength and density. In conjunction with the penetration testing, split-spoon soil
samples were recovered for soil classification and laboratory testing.
Boring logs reports are included in the Appendix.
4
1.2 Laboratory Services: The laboratory services provided for this project consisted of visual
classification of the soil samples by the project engineer. The color, texture, and plasticity
characteristics were used to identify each soil sample in general accordance with the Unified Soil
Classification System (USCS) soil identification guidelines. The results of the visual classifications
are presented on the boring logs included in the Appendix. The laboratory testing program included
Atterberg limits (ASTM D4318), natural water content (ASTM D2216), and wash 200 (ASTM
D1140).
Results of the laboratory tests are included in the Appendix.
2.0 PROJECT INFORMATION
2.1 Project Information: Based on the information provided to our office by NV5, it is our
understanding that the proposed project will consist of storm water improvement to replace
24”/30”/36” RCP with a precast box culvert. The main purpose of the geotechnical investigation
was to determine general conditions of the subsurface soil, presence of rock and groundwater
conditions at the site, and to obtain the necessary geotechnical information for design purposes.
Three (3) soil boring tests (SBT) were proposed for this project. See attachments for boring
locations.
2.2 Site Location and Description: The project site limits are located along Wintercrest Lane and
Arundel Drive in Charlotte, North Carolina.
3.0 SUBSURFACE CONDITIONS
3.1 Regional Geology:
The referenced site is located within the Charlotte Belt of the Piedmont Geologic Province.
According to the USGS Map of North Carolina (1985), the site is reportedly underlain mainly by
intrusive rock that consists of granitic rock (DOg). The Piedmont Province generally consists of hills
and ridges which are intertwined with an established system of draws and streams. The Piedmont
Province is predominately underlain by igneous rock (formed from molten material) and
metamorphic rock (formed by heat, pressure and/or chemical action), which were initially formed
during the Precambrian and Paleozoic eras.
The virgin soils encountered in this area are the residual product of in-place chemical weathering of
rock which was similar to the rock presently underlying the site. In areas not altered by erosion or
disturbed by the activities of man, the typical residual soil profile consists of clayey soils near the
surface, where soil weathering is more advanced, underlain by sandy silts and silty sands. The
boundary between soil and rock is not sharply defined. This transitional zone termed “partially
weathered rock” is normally found overlying the parent bedrock. Partially weathered rock is
defined, for engineering purposes, as residual material with Standard Penetration Resistances in
excess of 100 blows per foot. Weathering is facilitated by fractures, joints and by the presence of
less resistant rock types. Consequently, the profile of the partially weathered rock and hard rock is
quite irregular and erratic, even over short horizontal distances. Also, it is common to find lenses
and boulders of hard rock and zones of partially weathered rock within the soil mantle, well above
the general bedrock level. Based on our site reconnaissance, obvious rock outcroppings were
observed at the site.
5
3.2 Field Exploration: The subsurface conditions discussed in the following paragraphs and those
shown on the attached boring logs represent an estimate of the subsurface conditions. These are based
on interpretation of the field and laboratory data using normally accepted geotechnical engineering
judgments. Subsurface profiles for the project stratigraphy have been prepared for convenience
only and are included in the Appendix.
Strata breaks designated on the boring logs represent approximate boundaries between soil types.
The transitions between different soil strata are usually less distinct than those shown on the boring
logs. Although individual soil test borings are representative of the subsurface conditions at the boring
locations on the dates shown, they are not necessarily indicative of subsurface conditions at other
locations or at other times. Data from the specific soil test borings are shown on the individual boring
logs included in the Appendix.
3.3 Surface: Asphalt layer was encountered in all the boring locations and were measured to have a
thickness of approximately 4 inches.
3.4 Subsurface: The subsurface conditions at the site, as indicated by the borings generally consist of
silty SAND, and sandy CLAY underlain by partially weathered rock and bedrock. Partially
weathered rock (PWR) was encountered in all the boring locations at depths ranging from 16 to 19.5
feet below the existing ground surface elevation. Auger refusal was encountered on B-2. The
generalized subsurface conditions are described below. For soil descriptions and general stratification
at a particular boring location, the respective boring log should be reviewed.
3.5 Fill Soil: The fill soils encountered consisted of sandy CLAY and sandy SILT to depths ranging
from 0 to 2.5 feet below the existing ground surface. SPT N-values recorded in the fill soils ranged
from 8 to 9 blows per foot (bpf) with an average SPT-N value of approximately 8 blows per foot
(bpf).
3.6 Residual Soil: The residual soils encountered consisted of sandy CLAY to depths ranging from
2.5 to 19.5 feet below the existing ground surface. SPT N-values recorded in the residual soils ranged
from 0 to 50/1” blows per foot (bpf) with an average SPT-N value of approximately 50 blows per
foot (bpf).
3.7 Partially Weathered Rock: Soils that exhibited SPT N-values characteristic of partially
weathered rock (PWR) were encountered at the boring locations. Hard weathered rock is defined for
engineering purposes as residual material exhibiting SPT N values in excess of 50 blows per inch.
Soft weathered rock is defined as SPT N-values between 50 blows per 6 inches and 50 blows per
inch. When sampled, the PWR generally breaks down into sandy silt and silty sand with rock
fragments.
3.8 Auger Refusal: Auger refusal is defined as material that could not be penetrated with the drill
rig equipment used on the project. Auger refusal material may consist of large boulders, rock
ledges, lenses, seams or the top of parent bedrock. Auger refusal occurred in all three boring at
depths ranging from 16.0 to 19.5 feet during the drilling operation. For more detailed soil
descriptions and stratifications at a particular soil test boring, the respective boring log should be
reviewed.
3.9 Groundwater Observations: Groundwater measurements were attempted at the termination of
drilling. Borings were backfilled for safety at the end of drilling. Groundwater was encountered in
boring locations B-2, and B-3 at the end of drilling. The groundwater was encountered to depths from
9.5 to 16.9 feet below ground surface elevations (see boring logs for actual depths).
6
3.10 Laboratory Testing: For geotechnical considerations, select split-spoon samples from the soil
test borings were subjected to laboratory classification testing. This testing included natural water
content determinations (ASTM D2216), wash 200 (ASTM D1140), and Atterberg limits tests
(ASTM D4318). Based on the results of these tests, the soil samples were then classified in general
accordance with Unified Soil Classification System (ASTM D2487). A summary of test results is
provided in the Appendix.
4.0 PROJECT DESIGN AND CONSTRUCTION RECOMMENDATIONS
4.1 Site Preparation: Consultation with a geotechnical contractor is recommended before site
preparation. The proposed construction area transverses along Wintercrest Lane and Arundel Drive.
Based on the results of our subsurface exploration, and our understanding of the proposed
construction, the presence of rock fragments, partially weathered rock, and bedrock will likely to
be encountered. During construction, conventional construction equipment may not be able to
excavate the rock. It is anticipated that groundwater will influence construction at some locations
and may require dewatering applications.
Although there can be changes in the subsurface conditions over relatively short distances,
problems associated with excavating very dense soils are anticipated for this project. We have
generally found that material that our soil drilling augers can penetrate can also be excavated with a
large backhoe or ripped with a dozer mounted ripper.
4.2 Excavation: Based on the results of our subsurface exploration, it appears that the deeper on-
site soils, within the depths of the boring, may not be able to be excavated with conventional
construction equipment. Jack hammering or blasting may be required to achieve desired design
depths. Although there can be changes in the subsurface conditions over relatively short distances,
problems associated with excavating very dense soils may be anticipated for this project.
4.3 Fill Material and Placement: All fill used for the project should be free of organic matter and
debris with a low to moderate plasticity (Plasticity Index less than 30). The fill should exhibit a
maximum dry density of at least 90 pounds per cubic foot, as determined by a Standard Proctor
compaction test (ASTM D698). Fill material should remain stable under heavy pneumatic-tired
construction equipment. During site grading, some moisture modification (drying and/or wetting) of
the onsite soils will likely be required. Based on the results of our visual classifications and laboratory
testing program, the on-site silty SAND, and sandy CLAY appears suitable for use as project fill.
During construction, care should be taken to control the moisture content of the proposed fill soils.
All fill should be placed in lifts of 6 to 8 inches loose thickness and should be compacted to at least
95 percent of the soil’s standard Proctor maximum dry density. However, for isolated excavations
around footing locations or within utility excavations, a hand tamper will likely be required. While
using a hand tamper, the maximum lift thickness (loose) should not exceed 5 inches. We recommend
that field density tests be performed on the fill as it is being placed, at a frequency determined by an
experienced geotechnical engineer, to verify that proper compaction is achieved.
Soil placed as fill should be an approved material, free of organic matter or debris, and have a liquid limit and plasticity index less than 40 and 15, respectively. Depending on the moisture content at the time of placement, drying or wetting of the fill may be required to obtain the required compaction percentage. In-place density tests should be performed with a minimum of 1 test per 100 feet for each lift of fill placed. Moisture contents should be controlled by spreading out spoil piles to let dry
7
out to achieve the desired moisture content and density specifications. We recommend that all fill operations be observed by a qualified soil technician to determine if minimum compaction requirements are being met.
4.4 Cut and Fill Slopes: Permanent cut and properly compacted fill slopes should be no steeper than 2(H):1(V) without engineered reinforcement included and should be properly seeded to minimize erosion. For maintenance purposes, the permanent slopes may need to be flattened to allow access to maintenance equipment. Also, any fill placed in sloping areas should be properly benched into the adjacent soils. All excavations should conform to applicable OSHA regulations.
4.5 Plans and Specifications Review: We recommend that Capstone conduct a general review of
the final plans and specifications to evaluate that our site development recommendations have been
properly interpreted and implemented during design.
4.6 Fill Construction Observation and Testing: To effectively achieve the intent of the
geotechnical recommendations presented in this report and to maintain continuity from design
through construction, Capstone should be strongly considered to provide observation and testing
services during construction. This will provide Capstone with the opportunity to observe the
subsurface conditions encountered during construction, evaluate the applicability of the
geotechnical recommendations presented in our report as they relate to the soil conditions
encountered, and to provide follow up recommendations if conditions differ from those described
in our report.
5.0 CONCLUSION
Our evaluation has been based on our understanding of the project site, review of the project
information provided to our office, site visits, and the data obtained in our exploration. The borings
performed at this site represent the subsurface conditions at the location of the borings only. Due to
the prevailing geology, there can be changes in the subsurface conditions over relatively short
distances that have not been disclosed by the results of the borings performed. If the project
information is incorrect, or if the project description is changed, please contact us so that our
recommendations can be reviewed. The assessment of site environmental conditions for the presence
of pollutants in the soil, rock and groundwater of the site was beyond the scope of this exploration.
APPENDIX A
Figure 1 – Site Vicinity Map
Figure 2 – Boring Plan
SITE VICINITY MAP
Wintercrest Lane Storm Water Improvements Site
(Not to Scale)
Figure 1
General Site Location
Figure 2 Site Boring Location Plan
Wintercrest Lane/Arundel Drive
SB-2
SB-3
SB-4
B-1
B-2
B-3
APPENDIX B
Boring Logs
Bore Hole LogCapstoneT o : NV5
7500 East Indepence BlvdSuite 100Charlotte, NC 28227
P r o j e c t : Wintercrest Storm Water Improvements
Project Number: 100-19-058GReport Number: 1Report Date: 03-Dec-19Contractor: Breccia ConstructionDrill Method: H S A Technician: Cirilo SabaLogged By: Cirilo SabaDrill Date: 18-Nov-19Bore Hole Number: B1Location: Charlotte, NCHole Depth: 20 feetPage: 1 of 1
SPT Sample
Fee
t
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Moisture/Limits
N 3 6 9 12 15 18 21 24 27% 10 20 30 40
Plastic Limit (%)Natural Moisture (%)Liquid Limit (%)SPT Blow Count
Soil Description
0 to 2.5 - FILL STIFFGrey-Dark-Red CLAY withfine to coarse Sand
2.5 to 5 - FILL FIRMGrey-Dark-Red CLAY withfine to coarse Sand
5 to 7.5 - RESIDUAL VERYSOFT Dark- Grey-Brownfine to medium Sandy CLAY
7.5 to 10 - RESIDUAL VERYSOFT Brown-Grey CLAYwith fine to medium Sand.
10 to 15 - RESIDUALMEDIUM DENSE Green fineSandy SILT
15 to 19.5 - RESIDUALVERY DENSE GreenishGrey Silty fine to coarseSAND (PWR)
Sym
bo
l
Sam
ple
N
9
5
0
0
21
100+
Comments
Blow Counts
(5-4-5)
(2-3-2)
Weight of Hammer(WOH)
WOH
(8-10-11)
(44-50/5.5")
Boring Terminated @19.5ft
ID
1
2
3
4
5
6
USC
SC
SC
SC
SC
SM
SM
Bore Hole LogCapstone
T o : NV57500 East Independence BlvdSuite 100Charlotte, NC 28227
P r o j e c t : Wintercrest Sewer Improvement
Project Number: 100-19-058GReport Number: 1Report Date: 03-Dec-19Contractor:BRECCIA CONSTRUCTIONDrill Method: H S A Technician: Cirilo SabaLogged By: Cirilo SabaDrill Date: 18-Nov-19Bore Hole Number: B2Location: Charlotte, NCHole Depth: 20 feetPage: 1 of 1
SPT Sample
Fee
t
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Moisture/Limits
N 7 14 21 28 35 42 49 56 63% 10 20 30 40
Plastic Limit (%)Natural Moisture (%)Liquid Limit (%)SPT Blow Count
Soil Description
0 to 2.5 - FILL LOOSE Greenfine to coarse Sandy SILT
2.5 to 5 - RESIDUAL VERYSTIFF Brown-Green fineSandy CLAY
5 to 7.5 - RESIDUAL STIFFGrey-Brown CLAY with fineto coarse Sand
7.5 to 10 - RESIDUALMEDIUM DENSE Brown fineto coarse Sandy SILT
10 to 15 - RESIDUAL VERYDENSE Brown fine to coarseSandy SILT
15 to 16.10 - PWR
Sym
bo
l
Sam
ple
N
9
16
10
13
70
100+
Comments
Water Level 19-Nov-19,16.9 feet
Blow Counts
(5-4-5)
(4-6-10)
(3-4-6)
(4-4-9)
(9-24-46)
(50/1)
Auger Refusal @ 16.10ft
Boring Terminated @16.11ft
ID
1
2
3
4
5
6
USC
SM
SC
SC
SM
SM
Bore Hole LogCapstone
T o : NV57500 East Independence BlvdSuite 100Charlotte NC 28227
P r o j e c t : Wintercrest Sewer Improvement
Project Number: 100-19-058GReport Number: 1Report Date: 03-Dec-19Contractor:BRECCIA CONSTRUCTIONDrill Method: H S A Technician: Cirilo SabaLogged By: Cirilo SabaDrill Date: 18-Nov-19Bore Hole Number: B3Location: Charlotte, NCHole Depth: 20 feetPage: 1 of 1
SPT Sample
Fee
t
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Moisture/Limits
N 7 14 21 28 35 42 49 56 63% 10 20 30 40
Plastic Limit (%)Natural Moisture (%)Liquid Limit (%)SPT Blow Count
Soil Description
0 to 2.5 - FILL LOOSE Greenfine to coarse Sandy SILTwith Gravel
2.5 to 5 - RESIDUAL FIRMBrown-reddish-Yellow CLAYwith fine to medium Sand
5 to 7.5 - RESIDUAL FIRMBrown-Reddish-Yellow CLAYwith fine to medium Sand
7.5 to 10 - RESIDUAL FIRMBrown-Reddish-Yellow CLAYwith fine to medium Sand
10 to 15 - RESIDUAL VERYHARD Grey-Reddish-BrownCLAY with fine to mediumSand
15 to 19.5 - RESIDUALVERY HARD Brown-GreyCLAY with fine to mediumSand
Sym
bo
l
Sam
ple
N
8
5
6
7
61
87+
Comments
Water Level 19-Nov-19,9.5 feet
Blow Counts
(5-4-4)
(2-3-2)
(2-3-3)
(3-3-4)
(24-39-22)
(37-50/5.5")
Boring Terminated @19.5ft
ID
1
2
3
4
5
6
USC
SM
SC
SC
SC
SC
SC
APPENDIX C
Laboratory Test Summary Sheet
1
Project Name: 11/19/19
Project Number: Charlotte, NC
Capstone Project Number: CG2
Architect/Engineer:
Liquid Limit Plasticity Index
B-1 S3 Soil 29.5
S4 Soil 40.7 76.2 CL 38 21 17 114.2 14.5
S6 Soil 9.3
B-2 S2 Soil 17.9
S5 Soil 17.0
B-3 S3 Soil 24.4
S6 Soil 28.8 60.2 CL 42 20 22 113.5 15.2
Laboratory Test Results Summary
Maximum
Dry
Density
(pcf)
Optimum
Moisture
(%)
Page:
Passing
No. 200
Sieve (%)
Wintercrest Storm Water Improvements
ATTERBERG LIMITS
Plastic Limit
Sample
Type
USCS
Classification
Natural
Moisture
Content
(%)
-
Comments:
Date:
Project Location:
100-19-058
NV5 C. SabaTechnician:
Contractor:
Boring or
Sample
No.
Sample
Depth
(feet)
APPENDIX D
Supplemental Information
I. Drilling and Sampling Symbols:
SS - Split Spoon Sampler RB - Rock Bit Drilling
ST - Shelby Tube Sampler BS - Bulk Sample of Cuttings
RC - Rock Core: NX, BX, AX PA - Power Auger (no sample)
PM - Pressuremeter HAS - Hollow Stem Auger
DC - Dutch Cone Penetrometer WS - Wash Sample
WHO - Weight of Hammer
Standard Penetration (Blows/Ft) refers to the blows per foot of a 140 lb. hammer falling 30 inches on
a 2 inch O.D. split spoon sampler in ASTM D-1586. The blow count is commonly referred to as the
N-value.
II. Correlation of Penetration Resistances to Soil Properties:
Relative Density-Sands, Silts
SPT-N Relative Density N-Values Consistency of Cohesive Soils
0-4 Very Loose 0-2 Very Soft
5-10 Loose 3-4 Soft
11-30 Medium Dense 5-8 Firm
31-50 Dense 9-15 Stiff
50 or more Very Dense 16-30 Very Stiff
31-50 Hard
51 or more Very Hard
III. Unified Soil Classification Symbols:
CP - Poorly Graded Gravel ML - Low Plasticity Silts
GW - Well Graded Gravel MH - High Plasticity Silts
GM - Dirty Gravel CL - Low Plasticity Clays
GC - Clayey Gravels CH - High Plasticity Clays
SP - Poorly Graded Sands OL - Low Plasticity Organics
SW - Well Graded Sands OH - High Plasticity Organics
SM - Silty Sands CL-ML - Dual Classification
SC - Clayey Sands (Typical)
IV. Water Level Measurement Symbols:
WL - Water Level BCR - Before Casing Removal
WS - While Sampling ACR - After Casing Removal
WD - While Drilling WCI - With Casing Installed
The water levels are those water levels actually measured in the borehole at the times indicated by the
symbol. The measurements are relatively reliable when auguring, without adding fluids, in a granular soil.
In clays and plastic silt, the accurate determination of water levels may require several days for the water
level to stabilize. In such cases, additional methods of measurement are generally applied.
The elevations indicated on the boring logs should be considered approximate and were not determined
using accepted surveying techniques.
Reference Notes for Boring Logs
UNIFIED SOIL CLASSIFICATION SYSTEM
UNIFIED SOIL C LASSIFICATI ON SYSTEM
Criteria for Assigning Group Symbols and Group Names Using Laboratory Tests ASoil Classification
GroupSymbol Group Name B
Coarse-Grained Soils:More than 50% retainedon No. 200 sieve
Gravels:More than 50% ofcoarse fractionretained on No. 4 sieve
Clean Gravels:Less than 5% fines C
Cu ³ 4 and 1 £ Cc £ 3 E GW Well-graded gravel F
Cu < 4 and/or 1 > Cc > 3 E GP Poorly graded gravel F
Gravels with Fines:More than 12% fines C
Fines classify as ML or MH GM Silty gravel F, G, H
Fines classify as CL or CH GC Clayey gravel F, G, H
Sands:50% or more of coarsefraction passes No. 4sieve
Clean Sands:Less than 5% fines D
Cu ³ 6 and 1 £ Cc £ 3 E SW Well-graded sand I
Cu < 6 and/or 1 > Cc > 3 E SP Poorly graded sand I
Sands with Fines:More than 12% fines D
Fines classify as ML or MH SM Silty sand G, H, I
Fines classify as CL or CH SC Clayey sand G, H, I
Fine-Grained Soils:50% or more passes theNo. 200 sieve
Silts and Clays:Liquid limit less than 50
Inorganic:PI > 7 and plots on or above “A”line J
CL Lean clay K, L, M
PI < 4 or plots below “A” line J ML Silt K, L, M
Organic:Liquid limit - oven dried
< 0.75 OL Organic clay K, L, M, N
Liquid limit - not dried Organic silt K, L, M, O
Silts and Clays:Liquid limit 50 or more
Inorganic:PI plots on or above “A” line CH Fat clay K, L, M
PI plots below “A” line MH Elastic Silt K, L, M
Organic:Liquid limit - oven dried
< 0.75 OH Organic clay K, L, M, P
Liquid limit - not dried Organic silt K, L, M, Q
Highly organic soils: Primarily organic matter, dark in color, and organic odor PT PeatA Based on the material passing the 3-inch (75-mm) sieveB If field sample contained cobbles or boulders, or both, add “with cobbles
or boulders, or both” to group name.C Gravels with 5 to 12% fines require dual symbols: GW-GM well-graded
gravel with silt, GW-GC well-graded gravel with clay, GP-GM poorlygraded gravel with silt, GP-GC poorly graded gravel with clay.
D Sands with 5 to 12% fines require dual symbols: SW-SM well-gradedsand with silt, SW-SC well-graded sand with clay, SP-SM poorly gradedsand with silt, SP-SC poorly graded sand with clay
E Cu = D60/D10 Cc =6010
230
DxD
)(D
F If soil contains ³ 15% sand, add “with sand” to group name.G If fines classify as CL-ML, use dual symbol GC-GM, or SC-SM.
H If fines are organic, add “with organic fines” to group name.I If soil contains ³ 15% gravel, add “with gravel” to group name.J If Atterberg limits plot in shaded area, soil is a CL-ML, silty clay.K If soil contains 15 to 29% plus No. 200, add “with sand” or “with
gravel,” whichever is predominant.L If soil contains ³ 30% plus No. 200 predominantly sand, add
“sandy” to group name.MIf soil contains ³ 30% plus No. 200, predominantly gravel, add
“gravelly” to group name.NPI ³ 4 and plots on or above “A” line.OPI < 4 or plots below “A” line.P PI plots on or above “A” line.QPI plots below “A” line.
Geotechnical-Engineering Report
Geotechnical Services Are Performed for Specific Purposes, Persons, and ProjectsGeotechnical engineers structure their services to meet the specific needs of their clients. A geotechnical-engineering study conducted for a civil engineer may not fulfill the needs of a constructor — a construction contractor — or even another civil engineer. Because each geotechnical- engineering study is unique, each geotechnical-engineering report is unique, prepared solely for the client. No one except you should rely on this geotechnical-engineering report without first conferring with the geotechnical engineer who prepared it. And no one — not even you — should apply this report for any purpose or project except the one originally contemplated.
Read the Full ReportSerious problems have occurred because those relying on a geotechnical-engineering report did not read it all. Do not rely on an executive summary. Do not read selected elements only.
Geotechnical Engineers Base Each Report on a Unique Set of Project-Specific FactorsGeotechnical engineers consider many unique, project-specific factors when establishing the scope of a study. Typical factors include: the client’s goals, objectives, and risk-management preferences; the general nature of the structure involved, its size, and configuration; the location of the structure on the site; and other planned or existing site improvements, such as access roads, parking lots, and underground utilities. Unless the geotechnical engineer who conducted the study specifically indicates otherwise, do not rely on a geotechnical-engineering report that was:• not prepared for you;• not prepared for your project;• not prepared for the specific site explored; or• completed before important project changes were made.
Typical changes that can erode the reliability of an existing geotechnical-engineering report include those that affect: • the function of the proposed structure, as when it’s changed
from a parking garage to an office building, or from a light-industrial plant to a refrigerated warehouse;
• the elevation, configuration, location, orientation, or weight of the proposed structure;
• the composition of the design team; or• project ownership.
As a general rule, always inform your geotechnical engineer of project changes—even minor ones—and request an
assessment of their impact. Geotechnical engineers cannot accept responsibility or liability for problems that occur because their reports do not consider developments of which they were not informed.
Subsurface Conditions Can ChangeA geotechnical-engineering report is based on conditions that existed at the time the geotechnical engineer performed the study. Do not rely on a geotechnical-engineering report whose adequacy may have been affected by: the passage of time; man-made events, such as construction on or adjacent to the site; or natural events, such as floods, droughts, earthquakes, or groundwater fluctuations. Contact the geotechnical engineer before applying this report to determine if it is still reliable. A minor amount of additional testing or analysis could prevent major problems.
Most Geotechnical Findings Are Professional OpinionsSite exploration identifies subsurface conditions only at those points where subsurface tests are conducted or samples are taken. Geotechnical engineers review field and laboratory data and then apply their professional judgment to render an opinion about subsurface conditions throughout the site. Actual subsurface conditions may differ — sometimes significantly — from those indicated in your report. Retaining the geotechnical engineer who developed your report to provide geotechnical-construction observation is the most effective method of managing the risks associated with unanticipated conditions.
A Report’s Recommendations Are Not FinalDo not overrely on the confirmation-dependent recommendations included in your report. Confirmation-dependent recommendations are not final, because geotechnical engineers develop them principally from judgment and opinion. Geotechnical engineers can finalize their recommendations only by observing actual subsurface conditions revealed during construction. The geotechnical engineer who developed your report cannot assume responsibility or liability for the report’s confirmation-dependent recommendations if that engineer does not perform the geotechnical-construction observation required to confirm the recommendations’ applicability.
A Geotechnical-Engineering Report Is Subject to MisinterpretationOther design-team members’ misinterpretation of geotechnical-engineering reports has resulted in costly
Important Information about This
Subsurface problems are a principal cause of construction delays, cost overruns, claims, and disputes.
While you cannot eliminate all such risks, you can manage them. The following information is provided to help.
problems. Confront that risk by having your geo technical engineer confer with appropriate members of the design team after submitting the report. Also retain your geotechnical engineer to review pertinent elements of the design team’s plans and specifications. Constructors can also misinterpret a geotechnical-engineering report. Confront that risk by having your geotechnical engineer participate in prebid and preconstruction conferences, and by providing geotechnical construction observation.
Do Not Redraw the Engineer’s LogsGeotechnical engineers prepare final boring and testing logs based upon their interpretation of field logs and laboratory data. To prevent errors or omissions, the logs included in a geotechnical-engineering report should never be redrawn for inclusion in architectural or other design drawings. Only photographic or electronic reproduction is acceptable, but recognize that separating logs from the report can elevate risk.
Give Constructors a Complete Report and GuidanceSome owners and design professionals mistakenly believe they can make constructors liable for unanticipated subsurface conditions by limiting what they provide for bid preparation. To help prevent costly problems, give constructors the complete geotechnical-engineering report, but preface it with a clearly written letter of transmittal. In that letter, advise constructors that the report was not prepared for purposes of bid development and that the report’s accuracy is limited; encourage them to confer with the geotechnical engineer who prepared the report (a modest fee may be required) and/or to conduct additional study to obtain the specific types of information they need or prefer. A prebid conference can also be valuable. Be sure constructors have sufficient time to perform additional study. Only then might you be in a position to give constructors the best information available to you, while requiring them to at least share some of the financial responsibilities stemming from unanticipated conditions.
Read Responsibility Provisions CloselySome clients, design professionals, and constructors fail to recognize that geotechnical engineering is far less exact than other engineering disciplines. This lack of understanding has created unrealistic expectations that have led to disappointments, claims, and disputes. To help reduce the risk of such outcomes, geotechnical engineers commonly include a variety of explanatory provisions in their reports. Sometimes labeled “limitations,” many of these provisions indicate where geotechnical engineers’ responsibilities begin and end, to help
others recognize their own responsibilities and risks. Read these provisions closely. Ask questions. Your geotechnical engineer should respond fully and frankly.
Environmental Concerns Are Not Covered The equipment, techniques, and personnel used to perform an environmental study differ significantly from those used to perform a geotechnical study. For that reason, a geotechnical-engineering report does not usually relate any environmental findings, conclusions, or recommendations; e.g., about the likelihood of encountering underground storage tanks or regulated contaminants. Unanticipated environmental problems have led to numerous project failures. If you have not yet obtained your own environmental information, ask your geotechnical consultant for risk-management guidance. Do not rely on an environmental report prepared for someone else.
Obtain Professional Assistance To Deal with MoldDiverse strategies can be applied during building design, construction, operation, and maintenance to prevent significant amounts of mold from growing on indoor surfaces. To be effective, all such strategies should be devised for the express purpose of mold prevention, integrated into a comprehensive plan, and executed with diligent oversight by a professional mold-prevention consultant. Because just a small amount of water or moisture can lead to the development of severe mold infestations, many mold- prevention strategies focus on keeping building surfaces dry. While groundwater, water infiltration, and similar issues may have been addressed as part of the geotechnical- engineering study whose findings are conveyed in this report, the geotechnical engineer in charge of this project is not a mold prevention consultant; none of the services performed in connection with the geotechnical engineer’s study were designed or conducted for the purpose of mold prevention. Proper implementation of the recommendations conveyed in this report will not of itself be sufficient to prevent mold from growing in or on the structure involved.
Rely, on Your GBC-Member Geotechnical Engineer for Additional AssistanceMembership in the Geotechnical Business Council of the Geoprofessional Business Association exposes geotechnical engineers to a wide array of risk-confrontation techniques that can be of genuine benefit for everyone involved with a construction project. Confer with you GBC-Member geotechnical engineer for more information.
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Copyright 2015 by Geoprofessional Business Association (GBA). Duplication, reproduction, or copying of this document, or its contents, in whole or in part, by any means whatsoever, is strictly prohibited, except with GBA’s specific written permission. Excerpting, quoting, or otherwise extracting wording from this document
is permitted only with the express written permission of GBA, and only for purposes of scholarly research or book review. Only members of GBA may use this document as a complement to or as an element of a geotechnical-engineering report. Any other firm, individual, or other entity that so uses this document without
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