1

2015 World of Coal Ash (WOCA) Conference, May 5-7, 2015, Nashville, TN http://www.worldofcoalash.org/

Assessment of New QC/QA Compaction Monitoring Program at TVA’s Coal Combustion

Product Stacking Facilities: A Case Study

David J. White1, Pavana K. R. Vennapusa2, Eric Hageman3, Barry Christopher4, Nick McClung5, Roberto Sanchez6 1Geotechnical Consultant and R.L. Handy Professor, Iowa State University; 2Geotechnical Consultant and Research Assistant Professor, Iowa State University; 3Project Engineer at HDR Engineering, Inc.; 4Geotechnical Consultant, 5Geotechnical Engineering Manager at Tennessee Valley Authority; 6Geotechnical Consultant KEYWORDS: Coal Combustion Products, Fly Ash, Compaction, Intelligent Compaction, Specifications, Quality Control, Quality Assurance ABSTRACT Since 2012, The Tennessee Valley Authority (TVA) has been investigating new assessment techniques and specifications to improve the quality assessment process for its coal combustion product (CCP) impoundments and stacking facilities. As a result of initial field trials, a field demonstration project was setup at the TVA Shawnee Power Plant with the goals of improving field process control and reducing the risk of placing poorly compacted fly ash materials. Newly developed machine integrated measurement system (MiMS) that obtained measurements over nearly 100% of the compacted area, rapid in situ tests for measurement of moisture, density, and shear strength, and a field geotechnical mobile lab for onsite testing and evaluation of test results were setup for this project. In this paper, results obtained from placement of multiple lifts of fly ash material over a period of 3 months (May to August 2014) are presented. Results are presented as color-coded geospatial maps of MiMS measurements and control charts of in situ spot test measurements over time with a reference to the target requirements. Analysis of the findings shows that traditional moisture-density inspection does not provided statistically significant information related to compaction quality and that the current field placement process results in significant variability. The results and experience gained from this field demonstration were used develop recommendations for implementation plan on future TVA projects. (223 words).

2015 World of Coal Ash (WOCA) Conference in Nasvhille, TN - May 5-7, 2015http://www.flyash.info/

2

INTRODUCTION Tennessee Valley Authority (TVA) formed the Generation Construction Organization (GCO) immediately after the coal combustion production (CCP) dredge cell failure at its Kingston fossil-power generating facility in 2008. The main goal of the GCO is to manage engineering assessments and perform improvements to construction processes of its CCP impoundments and stacking facilities. In 2012, TVA began investigating new assessment techniques and specifications for quality control (QC) and quality assurance (QA) to improve the assessment processes and conducted field trails at two of its fossil-power generation plants (White et al. 2012a, 2012b). The field trials included evaluating the use of roller-integrated compaction monitoring technologies (i.e. intelligent compaction) and various in situ stiffness based point testing methods, and a critical review of the state of the practice of field and laboratory testing methods at the TVA facilities. The review raised several concerns with the current state of the practice and are summarized in Christopher et al. (2013) and White et al. (2013). The following were identified as some of the key concerns:

1) TVA process control standards in terms of moisture conditioning, lift thickness placement, compaction method(s), and QC/QA test methods vary significantly from plant to plant.

2) Inconsistent QC/QA in frequency of testing and documentation of placement procedures and compaction methods.

3) Field density test results typically met permit requirements, but were based on only a few characteristic moisture-density curves; however, CCP materials were found to be highly variable with a broad range of properties; thus, the data from QC tests are questionable.

4) A very broad range of moisture content measurements in compacted materials, much of which is outside the range of best practice, and, in some cases, technically were not feasible based on the characteristic moisture-density curves, again questioning the reliability of QC results.

5) In some cases, explorations conducted for the dry stack designs have encountered zones (planes) of weaker or wetter material within the existing stack profile, which has in some cases led to the use of conservative strength parameters.

As a result of the initial field trials and review, a field demonstration project was setup at the TVA Shawnee Power Plant with the goals of improving field process control and reducing the risk of placing poorly compacted fly ash materials. QA on the project included achieving a minimum of 95% of standard Proctor dry density and moisture content within -2% and +4% of standard Proctor optimum moisture content. Field tests are required at 2 tests per acre at randomly selected test locations. In the following sections, a brief overview of the project and the QC/QA testing process, an overview of testing methods, and results from field testing are provided. Based on results from this field demonstration, recommendations for implementation of the new QC/QA processes during construction of CCP stacking facilities are provided.

3

PROJECT OVERVIEW AND FIELD MONITORING PROCESS The project was in two phases. Phase I involved setting up a machine integrated measurement system (MiMS) on a vibratory compaction roller (Figure 1), a wheel loader to monitor wheel rutting, and a dump truck to monitor productivity; setting up an on-site geotechnical mobile laboratory (Figure 2); and develop field calibrations with in situ point testing methods. MiMS on the roller included recording compaction measurements, compaction productivity and quality, compaction guidance, and a video playback, along with the capability to automatically generate a compaction report. Also, standard operation procedures (SOPs) and safety guidelines for using laboratory and in situ testing procedures were developed.

Outputs include :

• CMV (vibration)

• CCV (vibration)

• XMV (vibration)

• Compaction Quality

• Compaction Productivity

• Compaction Guidance

• Video Playback

• Automated .csv file

Data viewable real-time via local mesh

network and remotely

Operator controls machine; Engineer

control setup.

Figure 1. Vibratory compaction roller setup with MiMS (top) and onboard display showing compaction data analytics (bottom)

4

Figure 2. TVA’s geotechnical mobile lab (top left), rapid moisture-balance testing devices (top right), unconfined compression/consolidation testing device (bottom

left), and Proctor testing (right) In Phase II, MiMS measurements on vibratory roller, which provided 100% coverage of the compacted area, and in situ spot tests to rapidly determine measurements of moisture, density, shear strength, and modulus were performed from May 17 to August 15, 2014. Moisture content was obtained using rapid moisture analyzers setup in the geotechnical mobile lab to determine moisture within 5 to 10 minutes as well as the standard oven-drying method. Density was obtained using the drive core (DC) method. Effective stress shear strength parameters cohesion and friction angle were obtained using borehole shear test (BST). Elastic modulus and California bearing ratio values were determined using plate load testing and dynamic cone penetrometer (DCP) testing, respectively. Pictures of the test methods are shown in Figure 3. The testing process involved collected a bulk sample during placement to conduct Proctor testing on-site within 4 hours of ash placement. Obtaining Proctor testing results

5

within this time frame was critical as the optimum moisture content and maximum dry unit weight values were observed to decrease with increasing mellowing time due to chemical reactions as described in the companion paper (White et al. 2015). After placement and compaction operations were completed by the contractor, the compacted area was mapped using the calibrated MiMS vibratory compaction roller. After mapping, three to five locations were selected based on the MiMS map representing low, medium, and high values of roller-integrated compaction measurement value (CMV), to conduct DC, BST, and DCP testing. All testing was performed within the same day or the day after compaction was performed.

Figure 3. DCP testing (top left), DC testing (top right), BST (bottom left), and shear head after testing (bottom right)

6

TESTING METHODS Proctor Compaction Testing Standard Proctor compaction testing was conducted in accordance with ASTM D698-10. Samples were prepared at 6 to 8 desired target moisture contents and compacted within 4 hours of fill placement. Drive Core Density and Moisture Content Drive core (DC) testing was performed to determine in situ density and moisture content in accordance with ASTM D2937-10. After excavating the sample from the ground, the drive core was carefully sealed in a zip-loc bag and was immediately transported to the mobile laboratory for testing. Total unit weight of the material was determined and moisture content of the representative sample was obtained using oven-drying test procedure (at 60 oC and/or 110oC. The temperature for drying was selected based on thermo-gravimetric analysis (TGA) described in the companion paper (White et al. 2015). Dynamic Cone Penetrometer DCP tests were conducted in accordance with ASTM D6951-03. The tests involve dropping a 8 kg hammer from a height of 57.4 cm. and measuring the resulting penetration depth. The penetration depth and the number of blows were automatically recorded in the device. Based on the penetration depth and the number of blows, the penetration index (PI) values in units of mm/blow or in/blow are calculated. Using the PI values, California bearing ratio (CBR) and elastic modulus (E) were calculated using the following equations: DCP-CBR (%) = 292/PI1.12 (ASTM D6951-03) (1) DCP-E (ksi) = 2.555 (DCP-CBR)0.64 (Powell et al. 1984) (2) The calculations resulted in a profile of DCP-CBR and DCP-E values with depth. In this paper, an average of the top 12 in. (304 mm) was determined using PI values calculated as 304 mm divided by the cumulative number of blows took to reach the 304 mm depth. Bore Hole Shear Test BSTs were performed per manufacturer guidelines to determined drained cohesion and friction angle values of the material in situ (Handy Geotechnical Instruments, Inc., 2013). Test setup is shown in Figure 3. The test involved preparing a 2.8 in. cavity using a drop hammer and a shelby tube down to a depth of about 1 to 1.5 ft below surface,

7

and conducting the test by placing the shear head in the cavity. The test involved applying a 7.3 psi (50 kPa) normal stress and allowing for about 3 minute consolidation time and applying shearing stresses until it reaches a peak value. The peak shear stress and the normal stress are recorded. Then the test procedure was repeated for 14.5 psi and 21.8 psi normal stresses. Using the results, shear stress and normal stress plots were generated to determine cohesion and friction angle values. An example data set for three tests is provided in Figure 4. The main advantage of BST is that the drained friction angle and cohesion values developed from this test can be obtained within < 15 minutes as compared to several days using laboratory testing.

NORMAL STRESS, PSI

0 5 10 15 20 25 30

SH

EA

R S

TR

ES

S, P

SI

0

5

10

15

20

25

30

MAP14-A

MAP14-D

MAP14-E

Date: 06/26/2014

Tested By: EH/JR

Sample Location: MAP14-A,D*,E*

Material: Fly Ash and Sluice*

Test Method: Manufacturer Standard

MAP14-ACohesion, PSI 0.97

Friction Angle, DEG: 33.4

MAP14-DCohesion, PSI 1.55

Friction Angle, DEG: 29.2

MAP14-ECohesion, PSI 0.73

Friction Angle, DEG: 31.8

Figure 4. BST results from MAP 14.

Compaction Meter Value CMV is a dimensionless compaction parameter developed by Geodynamik in the late 1970s that depends on roller dimensions, (i.e., drum diameter and weight) and roller operation parameters (e.g., frequency, amplitude, speed), and is determined using the dynamic roller response (Sandström 1994). It is calculated using Eq. 3, where C is a

constant (300), A2 = the acceleration of the first harmonic component of the vibration,

A = the acceleration of the fundamental component of the vibration (Sandström and Pettersson 2004). It is well-documented in the literature that CMV correlates better with strength or stiffness based measurements than with dry density (White et al. 2011).

A

AC CMV 2 (3)

8

FIELD MONITORING RESULTS The contractor typically placed 1,000 to 2,000 tons of ash per day (Figure 5). Ash was placed during 48 days over the 3 month monitoring period (May 17 to August 14, 2014). Picture of ash placement and spreading are shown in Figure 6. Occasionally, dredged sluice was included as part of the fill. A Komatsu WD600 wheel dozer was used to spread and also served as the primary compaction method for the material. The contractor was trained on-site to use the MiMS roller to map the compacted areas. Target values were selected for CMV results using on-site plate load tests per AASHTO T222. Geo-referenced CMV measurements (via RTK-GPS) with 100% coverage were produced. The 24 maps obtained from the project are combined and are shown in Figure 7 along with in situ point test locations where DCP, DC, and BSTs were performed. As an example for one map (Figure 8), DCP-CBR test results at locations showing low, medium, and high CMV values are shown in Figure 9. Standard Proctor maximum dry density and optimum moisture content results over the monitoring period are shown in Figure 10. Results indicated that the Proctor results changed significantly over time with dry density varying from about 65 to 80 pcf and optimum moisture content varying from about 25% to 45%. These changes are attributed to changes in the chemical composition of the fill material. Control charts of in situ relative compaction (calculated as in situ dry density divided by standard Proctor maximum dry density) and moisture contents relative to the standard Proctor optimum moisture content are shown in Figure 11, with reference to the QA target limits. Results indicated that about 40% of the tests were below the target 95% minimum relative compaction and about 79% of the tests were outside the target relative moisture content limits.

Date

05/19/14 06/02/14 06/16/14 06/30/14 07/14/14 07/28/14 08/11/14

Qu

an

tity

of

Fly

As

h/D

ay,

To

ns

0

500

1000

1500

2000

2500

3000

Figure 5. Quantity of fly ash placed per day

9

Figure 6. Pictures of ash placement and spreading/compaction operations (top left, top right, and bottom left) and dredged sluice fill (bottom right)

10

7

11

15

20

>20

CMV MAPS 1 to 24

CMV

MAPS 1 to 24

In Situ Test

Points

Figure 7. Geo-referenced color-coded spatial map of CMV combining maps 1 to 24 overlaid with in situ test points

11

Legend

CS74

LastCMV

" <10

" 10-15

" 15-20

" 20-30

" 30-40

(6)(12)(2)

Figure 8. Geo-referenced color-coded spatial map of CMV with in situ test point locations

CBR (%)

1 10 100

De

pth

(m

m)

0

100

200

300

400

500

Pt (6) - SOFT

Pt (12) - HARD

Pt (2) - MEDIUM

Cumulative Blows

0 20 40 60 800

100

200

300

400

500

Pt (6) - SOFT

Pt (12) - HARD

Pt (2) - MEDIUM

Figure 9. DCP-CBR test results with depth at three locations

.

12

05/19/14 06/02/14 06/16/14 06/30/14 07/14/14 07/28/14 08/11/14

Std

. P

roc

tor

Ma

xim

um

De

ns

ity,

PC

F

60

65

70

75

80

85

90

05/19/14 06/02/14 06/16/14 06/30/14 07/14/14 07/28/14 08/11/14

Std

. P

roc

tor

Op

tim

um

M

ois

ture

Co

nte

nt,

%

20

25

30

35

40

45

Date

05/19/14 06/02/14 06/16/14 06/30/14 07/14/14 07/28/14 08/11/14

Sp

ec

ific

Gra

vit

y

2.1

2.2

2.3

2.4

2.5

Figure 10. Laboratory standard Proctor maximum dry density, optimum moisture content, and specific gravity test results

The results illustrate that, due to the variability of the material and its compaction properties, the current practice of occasionally sampling and testing to establish target values and random testing for field densities and moisture contents is inadequate. Also, the target dry density and moisture contents are surrogate measurements and do not directly link with the design parameters (i.e., stiffness or strength measurements). MiMS measurements has the advantage of providing full coverage over the compacted area, but have to be calibrated to in situ measurements that are related to design values.

13

Date

05/19/14 06/02/14 06/16/14 06/30/14 07/14/14 07/28/14 08/11/14

In S

itu

Rela

tive C

om

pa

cti

on

, %

70

80

90

100

110

120

130

Date

05/19/14 06/02/14 06/16/14 06/30/14 07/14/14 07/28/14 08/11/14

In S

itu

Rela

tive M

ois

ture

Co

nte

nt,

%

-20

-10

0

10

20

Min. Target Relative Comapction = 95%

Moisture Control Limits = -4 to +2%of Std. Proctor optimimum

Total # of measurements = 102# of measurements < 95% RC = 41

Total # of measurements = 545# of measurements outside control limits = 428

Figure 11. Control charts of in situ relative compaction and relative moisture content test results

SUMMARY OF KEY OUTCOMES A summary of key outcomes from the project were as follows:

• MiMs and in situ testing methods to rapidly determine moisture content, dry density, shear strength, and modulus demonstrated that the placement of ash materials should require careful process control and that results can be variable.

• MiMS was setup within a day and the contractor required minimal amount of time for training to operator the roller and record the maps.

• Collection of data that provides 100% coverage and automated report generation can be a significant improvement over the current QC/QA documentation practice.

• The ash contractor performed mapping passes and provided positive feedback in terms of having information available real-tie to assess compaction quality.

14

• Field test results indicated that, due to the variability of the materials and its compaction properties, the current practice of relatively infrequent sampling and testing to establish target values and random testing for field densities and moisture contents does not reduce risk of placing materials outside the establish control criteria.

• The target dry density and moisture contents are surrogate measurements and do not directly link with the design parameters (i.e., stiffness or strength measurements). MiMS measurements has the advantage of providing full coverage over the compacted area, but have to be calibrated to in situ measurements that are related to design.

• MiMS measurements, if properly calibrated, can potentially reduce the number of QA tests to be performed.

RECOMMENDATIONS FOR FUTURE IMPLEMENTATION A summary of recommendations from this study are as follows:

Establish a MiMs implementation team that can develop site-specific QC/QA specification guidelines.

Implement MiMs mapping via rollers to reduce risk by carrying out site/machine specific calibration with design related parameters.

Setup on-site lab staffed with field engineer to document QA testing including DCP, DC, and/or BST at areas of non-compliance as identified in calibrated MiMs maps.

Provide training to field personnel/contractor during the setup phase.

Use laboratory micro-analysis testing such and thermos gravimetric analysis (TGA) to identify the chemical composition of the materials.

Develop site specific compaction improvement plans.

Explore adding MiMs to additional equipment as needed to improve field control (i.e., water truck, other compaction equipment, etc.).

REFERENCES Christopher, B.R., White, D.J., Sanchez, R.L. (2013). “Proposed Compaction QC/QA Specifications for TVA’s CCP Stacking Facilities: Part 1. Evaluation of Performance Requirements,” 2013 World of Coal Ash (WOCA) Conference, April 22-25, Lexington, KY. Handy Geotechnical Instruments, Inc., (2013). “Borehole Shear Test Instructions Manual,” Handy Geotechnical Instruments, Inc., Madrid, Iowa. Sandström, Å. (1994). Numerical simulation of a vibratory roller on cohesionless soil, Internal Report, Geodynamik, Stockholm, Sweden.

15

Sandström A.J., and Pettersson, C.B. (2004). "Intelligent systems for QA/QC in soil compaction", Proc., 83rd Annual Transportation Research Board Meeting, January 11-14. Washington, D.C. White, D.J., Christopher, B.R., Sanchez, R.L. (2013). “Performance Based QC/QA Specifications for TVA’s CCP Stacking Facilities: Part II. Proposed Specifications,” 2013 World of Coal Ash (WOCA) Conference, April 22-25, Lexington, KY. White, D.J, Vennapusa, P., and Gieselman, H. (2011). “Field Assessment and Specification Review for Roller-Integrated Compaction Monitoring Technologies,” Advances in Civil Engineering, Vol. 2011, Article ID 783836,doi:10.1155/2011/783836. White, D.J., Vennapusa, P., Gieselman, H., Miller, K., Harland, J. (2012a). “Quality Compaction Field Research: TVA Widows Creek Fossil Plant,” Final Report Submitted to TVA, Center for Earthworks Engineering Research, Iowa State University, Ames, IA. White, D.J., Vennapusa, P., Gieselman, H., Miller, K., Harland, J. (2012b). “Quality Compaction Field Research: TVA Cumberland Creek Fossil Plant,” Final Report Submitted to TVA, Center for Earthworks Engineering Research, Iowa State University, Ames, IA. White, D.J., Vennapusa, P., Hageman, E., Christopher, B., McClung, N. (2015). “Effects of Micromorphology and Chemical Composition on Densification of CCPs,” 2015 World of Coal Ash (WOCA) Conference, May 5-7, Nashville, TN.