2601_CumberlandCoMSWLF_20171006_PTCRevisionInterfaceFrictionAngle_DIN28558

5400 Glenwood Avenue, Suite 400
Raleigh, North Carolina 27612
tel: [phone]
fax: [phone]

October 6, 2017

Mr. Ming-Tai Chao
North Carolina Department of Environmental Quality
Division of Waste Management
Solid Waste Section
1646 Mail Service Center
Raleigh, North Carolina 27699-1646

Subject: Ann Street MSW Landfill
Cumberland County, North Carolina
Phase IV Permit to Construct Application
Permit No. 2601-MWSLF-1997
Revision Request

Dear Mr. Chao:
On behalf of Cumberland County, CDM Smith is requesting a revision to a requirement in the Phase
IV Permit to Construct Application approved by the Solid Waste Section on December 29, 2016. As
discussed in the Geotechnical Report (Part 3: Engineering Plan – Appendix D) and the Construction
Quality Assurance (CQA) Plan (Part 4: CQA Plan – Appendix A), the interface friction angle between
the compacted clay liner and the textured 60-mil high density polyethylene (HDPE) geomembrane
liner was specified to be at least 21 degrees. Per the Conformed Project Specifications, the interface
friction angle between the compacted clay liner and the HDPE textured liner was analyzed in
accordance with ASTM D5321 “Standard Test Method for Determining the Shear Strength of Soil-
Geosynthetic and Geosynthetic-Geosynthetic Interfaces by Direct Shear.” The sample demonstrated
a friction angle of 15.5 degrees as documented in the test result provided in Attachment A.
The initial friction angle of 21 degrees presented in the Permit to Construct (PTC) Application was
based on typical values used in previous projects with similar material types. Based on the actual
test data for the clay material used for this project, a CDM Smith geotechnical engineer reviewed the
geotechnical evaluation and determined that a revised minimum interface friction angle of 15
degrees between the compacted clay liner and textured HDPE liner would still be sufficient to meet
the minimum acceptable factor of safety for overall global stability of 1.5 under static loading
conditions. Copies of the revised global stability analyses are provided in Attachment B.
In order to continue use of the selected clay source which conforms to all other project
specifications, CDM Smith would like to revise the construction materials conformance requirement
from an interface friction angle of 21 degrees to 15 degrees. As stated above, a revision of the

Attachment A
Interface Friction Test Results

544 Braddock Avenue • East Pittsburgh, PA 15112 • Phone [phone] • Fax [phone] • www.geotechnics.net

INTERFACE FRICTION TEST RESULTS
ASTM D 5321
CLIENT : ECS Southeast, LLP
CLIENT PROJECT : St. Ann Landfill
PROJECT NO. : L17146-02
LAB I. D. NO.: Clay Blend, (L17146-01-01)
Agru 60 mil HDPE Microspike, Roll # G17F002477 (L17146-01-02)
INTERFACE :Clay @ 94.8 pcf & 24.7% M.C.
vs. 60 mil HDPE Microspike (Bottom Side)
PEAK SHEAR RESIDUAL SHEAR
FRICTION ANGLE (deg) : Φ =15.5 Φ =12.0
COEFFICIENT OF FRICTION : = 0.278 = 0.213
ADHESION [Calculated] (psf): a = 88 a = 102
NOTES: 1.) Soil placement was based on 96 % maximum dry density & + 3% optimum moisture content.
2.) The interface was loaded, inundated with water & seated for 24 hours prior to placement.
3.) The peak friction angle was calculated using linear regression on the four data points.
4.) The residual friction angle was calculated using linear regression on the end of test values.
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y = 0.2779x + 87.66
y = 0.2134x + 102.46
0
2000
4000
6000
8000
10000
0 2000 4000 6000 8000 10000 12000 14000SHEAR STRESS (psf)NORMAL COMPRESSIVE STRESS (psf)
PEAK SHEAR DATA RESIDUAL SHEAR DATA

544 Braddock Avenue • East Pittsburgh, PA 15112 • Phone [phone] • Fax [phone] • www.geotechnics.net

INTERFACE FRICTION TEST RESULTS
ASTM D 5321
CLIENT : ECS Southeast, LLP
CLIENT PROJECT : St. Ann Landfill
PROJECT NO. : L17146-02
LAB I. D. NO.: Clay Blend, (L17146-01-01)
Agru 60 mil HDPE Microspike, Roll # G17F002477 (L17146-01-02)
INTERFACE :Clay @ 94.8 pcf & 24.7% M.C.
vs. 60 mil HDPE Microspike (Bottom Side)
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0
500
1000
1500
2000
2500
3000
3500
0.000 0.500 1.000 1.500 2.000 2.500 3.000SHEAR RESISTANCE (psf)HORIZONTAL DISPLACEMENT (in.)
SHEAR RESISTANCE VS HORIZONTAL DISPLACEMENT
144 psf NORMAL COMPRESSIVE STRESS
2,880 psf NORMAL COMPRESSIVE STRESS
5,760 psf NORMAL COMPRESSIVE STRESS
11,520 psf NORMAL COMPRESSIVE STRESS

544 Braddock Avenue • East Pittsburgh, PA 15112 • Phone [phone] • Fax [phone] • www.geotechnics.net

INTERFACE FRICTION TEST RESULTS
ASTM D 5321
CLIENT : ECS Southeast, LLP
CLIENT PROJECT : St. Ann Landfill
PROJECT NO. : L17146-02
LAB I. D. NO.S: Clay Blend, (L17146-01-01)
Agru 60 mil HDPE Microspike, Roll # G17F002477 (L17146-01-02)
INTERFACE :Clay @ 94.8 pcf & 24.7% M.C.
vs. 60 mil HDPE Microspike (Bottom Side)
STRAIN RATE (in/min) :0.008 DIRECT SHEAR UNIT: Durham Geo
PLACEMENT CONDITION:Inundated NORMAL LOAD: Bladder System
NORMAL LOAD (psf)2880 NORMAL LOAD (psf)5760 NORMAL LOAD (psf)11520
PEAK SHEAR STRESS (psf)906 PEAK SHEAR STRESS (psf)1735 PEAK SHEAR STRESS (psf)3262
PEAK SECANT ANGLE (deg)17.5 PEAK SECANT ANGLE (deg)16.8 PEAK SECANT ANGLE (deg)15.8
RESIDUAL SHEAR (psf)796 RESIDUAL SHEAR (psf)1413 RESIDUAL SHEAR (psf)2502
RESID. SECANT ANGLE (deg)15.5 RESID. SECANT ANGLE (deg)13.8 RESID. SECANT ANGLE (deg)12.3
ASPERITY 34 ASPERITY 35 ASPERITY 34
HORIZONTAL HORIZONTAL HORIZONTAL
DISPLACE. SHEAR FORCE STRESS DISPLACE. SHEAR FORCE STRESS DISPLACE. SHEAR FORCE STRESS
(in.)(lbs)(psf)(in.)(lbs)(psf)(in.)(lbs)(psf)
0.000 0 0 0.000 0 0 0.000 0 0
0.005 32 32 0.005 20 20 0.005 22 22
0.023 305 305 0.023 324 324 0.023 249 249
0.038 316 316 0.038 708 708 0.038 314 314
0.060 483 483 0.060 1039 1039 0.060 735 735
0.080 592 592 0.080 1253 1253 0.080 1528 1528
0.100 678 678 0.100 1399 1399 0.100 2093 2093
0.130 737 737 0.120 1512 1512 0.120 2495 2495
0.140 791 791 0.140 1589 1589 0.140 2754 2754
0.160 830 830 0.160 1648 1648 0.160 2974 2974
0.180 862 862 0.180 1697 1697 0.180 3128 3128
0.200 883 883 0.200 1724 1724 0.200 3220 3220
0.250 906 906 0.250 1735 1735 0.250 3262 3262
0.300 891 891 0.300 1696 1696 0.300 3191 3191
0.350 872 872 0.350 1659 1659 0.350 3104 3104
0.400 850 850 0.400 1629 1629 0.400 3014 3014
0.450 829 829 0.450 1591 1591 0.450 2957 2957
0.550 810 810 0.550 1549 1549 0.550 2891 2891
0.600 804 804 0.600 1535 1535 0.600 2853 2853
0.650 800 800 0.650 1518 1518 0.650 2818 2818
0.700 799 799 0.700 1514 1514 0.700 2783 2783
0.750 795 795 0.750 1495 1495 0.750 2751 2751
0.816 793 793 0.800 1481 1481 0.800 2745 2745
0.850 794 794 0.850 1485 1485 0.850 2724 2724
0.900 789 789 0.900 1472 1472 0.900 2695 2695
1.010 793 793 1.010 1471 1471 1.010 2675 2675
1.200 795 795 1.200 1455 1455 1.200 2611 2611
1.400 790 790 1.400 1444 1444 1.400 2598 2598
1.530 792 792 1.530 1443 1443 1.530 2570 2570
1.800 793 793 1.800 1438 1438 1.800 2546 2546
2.000 796 796 2.000 1430 1430 2.000 2535 2535
2.200 797 797 2.200 1433 1433 2.200 2516 2516
2.400 798 798 2.400 1436 1436 2.400 2504 2504
2.600 797 797 2.600 1427 1427 2.600 2504 2504
2.800 798 798 2.800 1426 1426 2.800 2507 2507
3.000 796 796 3.000 1413 1413 3.000 2502 2502
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544 Braddock Avenue • East Pittsburgh, PA 15112 • Phone [phone] • Fax [phone] • www.geotechnics.net

INTERFACE FRICTION TEST RESULTS
ASTM D 5321
CLIENT : ECS Southeast, LLP
CLIENT PROJECT : St. Ann Landfill
PROJECT NO. : L17146-02
LAB I. D. NO.S: Clay Blend, (L17146-01-01)
Agru 60 mil HDPE Microspike, Roll # G17F002477 (L17146-01-02)
INTERFACE :Clay @ 94.8 pcf & 24.7% M.C.
vs. 60 mil HDPE Microspike (Bottom Side)
STRAIN RATE (in/min) :0.008 DIRECT SHEAR UNIT: Durham Geo
PLACEMENT CONDITION:Inundated NORMAL LOAD: Bladder System
NORMAL LOAD (psf)144
PEAK SHEAR STRESS (psf)91
PEAK SECANT ANGLE (deg)32.1
RESIDUAL SHEAR (psf)59
RESID. SECANT ANGLE (deg)22.2
ASPERITY 33
HORIZONTAL
DISPLACE. SHEAR FORCE STRESS
(in.) (lbs) (psf)
0.000 0 0
0.005 2 2
0.023 8 8
0.038 17 17
0.060 34 34
0.080 46 46
0.100 52 52
0.120 57 57
0.140 60 60
0.160 63 63
0.180 66 66
0.200 68 68
0.250 73 73
0.300 77 77
0.350 80 80
0.420 82 82
0.450 85 85
0.550 89 89
0.600 91 91
0.650 89 89
0.700 85 85
0.750 81 81
0.800 77 77
0.850 74 74
0.900 72 72
1.010 70 70
1.200 66 66
1.400 64 64
1.530 63 63
1.800 61 61
2.000 60 60
2.200 59 59
2.400 59 59
2.600 58 58
2.800 59 59
3.000 59 59
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Attachment B
Slope Stability Analyses
1.7Top EL 254EL 250EL 250 Client: Cumberland County Project: Subtitle D Landfill ExpansionEL 90Composite Liner System24" Clay Liner24" Drainage SandWASTE24" Protective CoverWestCape Fear FormationEastAlluvial SandAlluvial ClayEL 100Cumberland County Subtitle D Landfill Expansion Slope Stability Analyses (Revised on 10/6/2017)Computed By: Wen, Jintao Date & Time: 10/6/2017 12:39:26 PMEL 97EL 88EL 79EL 871V4H4H1VEL 80EL 52Horizontal Distance(ft)0 100 200 300 400 500 600 700 800 900 1,000 1,100 1,200 1,300 1,400 1,500 1,600 1,700Elevation-60-40-20020406080100120140160180200220240260280300Elevation (feet)-60-40-20020406080100120140160180200220240260280300
1.7Top EL 254EL 250EL 250 Client: Cumberland County Project: Subtitle D Landfill ExpansionEL 90Composite Liner System24" Clay Liner24" Drainage SandWASTE24" Protective CoverWestCape Fear FormationEastAlluvial SandAlluvial ClayEL 100Cumberland County Subtitle D Landfill Expansion Slope Stability Analyses (Revised on 10/6/2017)Computed By: Wen, Jintao Date & Time: 10/6/2017 12:39:26 PMEL 97EL 88EL 79EL 871V4H4H1VEL 80EL 52Horizontal Distance(ft)0 100 200 300 400 500 600 700 800 900 1,000 1,100 1,200 1,300 1,400 1,500 1,600 1,700Elevation-60-40-20020406080100120140160180200220240260280300Elevation (feet)-60-40-20020406080100120140160180200220240260280300
1.8Top EL 254EL 250EL 250 Client: Cumberland County Project: Subtitle D Landfill ExpansionEL 90Composite Liner System24" Clay Liner24" Drainage SandWASTE24" Protective CoverWestCape Fear FormationEastAlluvial SandAlluvial ClayEL 100Cumberland County Subtitle D Landfill Expansion Slope Stability Analyses (Revised on 10/6/2017)Computed By: Wen, Jintao Date & Time: 10/6/2017 12:39:26 PMEL 97EL 88EL 79EL 871V4H4H1VEL 80EL 52Horizontal Distance(ft)0 100 200 300 400 500 600 700 800 900 1,000 1,100 1,200 1,300 1,400 1,500 1,600 1,700Elevation-60-40-20020406080100120140160180200220240260280300Elevation (feet)-60-40-20020406080100120140160180200220240260280300
1.9Top EL 254EL 250EL 250 Client: Cumberland County Project: Subtitle D Landfill ExpansionEL 90Composite Liner System24" Clay Liner24" Drainage SandWASTE24" Protective CoverWestCape Fear FormationEastAlluvial SandAlluvial ClayEL 100Cumberland County Subtitle D Landfill Expansion Slope Stability Analyses (Revised on 10/6/2017)Computed By: Wen, Jintao Date & Time: 10/6/2017 12:39:26 PMEL 97EL 88EL 79EL 871V4H4H1VEL 80EL 52Horizontal Distance(ft)0 100 200 300 400 500 600 700 800 900 1,000 1,100 1,200 1,300 1,400 1,500 1,600 1,700Elevation-60-40-20020406080100120140160180200220240260280300Elevation (feet)-60-40-20020406080100120140160180200220240260280300

Attachment C
Revised Sections of the Permit to Construct Application
Section 5 · Geotechnical Engineering Evaluation and Design Recommendations

5-6
Seciton 5.docx
Table 5-3: Soil and Landfill Parameters for Slope Stability Analyses
Material Unit Weight
(pcf)
Friction
Angle
(degrees)
Cohesion
(psf) Basis for Parameter Selection
Erosion Cover Sand 120 30 0 Previous Studies
Protective Cover
Layer 120 30 0 Specified Placement and
Compaction Methods
Geocomposite
Drainage Net & LLDPE
Liner
59 21 0 Veneer Stability Results
Waste 65 27.5 0 Literature Search
Protective Sand Layer 120 30 0 Specified Placement and
Compaction Methods
Geocomposite
Drainage Net & HDPE
Liner
59 21 (2) 0 Literature Search
Compacted Clay Liner 110 15 (3), 21 (4) 0 Previous Studies
Compacted Fill Layer 125 32 0 Specified Placement and
Compaction Methods
Alluvial Sand 115 30 0 Correlation from N-values
Alluvial Clay 120 26 150 Correlation from N-values and
Triaxial test results
Cape Fear Formation 120 35 0 Correlation from N-values
Notes:
1. Contract Documents should specify that the closure cap system components will have a minimum
interface friction angle of 20.5 degrees for 4H:1V slopes.
2. Contract Documents should specify that the liner system components will have a minimum interface
friction angle of 21 degrees.
3. Contract Documents should specify that the interface friction angle between the compacted clay liner and
HDPE liner shall be a minimum of 15 degrees.
4. Contract Documents should specify that the compacted clay liner will have a minimum internal friction
angle of 21 degrees.

5.2.3 Landfill Design Properties
The final landfill components will consist of the following in order of their occurrence below final
closure grade:
· 6-inch Erosion Cover Sand,
· 18-inch Protective Cover Layer,
Section 5 · Geotechnical Engineering Evaluation and Design Recommendations

5-7
Seciton 5.docx
· Geocomposite Drainage Net,
· 40-mil LLDPE Liner,
· 12-inch Intermediate Cover Layer,
· Waste,
· 24-inch Protective Sand Layer,
· Geocomposite Drainage Net,
· 60-mil HDPE Liner,
· 24-inch Compacted Clay Liner.
The assumed design properties for each component are listed in Table 5-3. The interface friction
angles of the actual liner system components should be measured under flooded conditions for the
compacted clay liner, GCL (if used), geomembrane, composite drainage net, and protective sand to be
used in the liner system prior to construction to demonstrate that the minimum required interface
friction angle is achieved for each interface. Interface friction angle testing should be conducted in
accordance with ASTM D5321 "Standard Test Method for Determining the Coefficient of Soil and
Geosynthetic or Geosynthetic and Geosynthetic Friction by the Direct Shear Method." Normal
stresses for the testing should represent anticipated field conditions.
5.2.4 Analyses
Analyses for overall (global) stability were performed using the SLOPE/W version 2007 modeling
software package distributed by GEO-SLOPE International, Ltd. This computer program uses the
inputted slope geometry, soil and waste properties, and groundwater conditions to calculate a factor
of safety against overall failure of the landfill mass. The minimum acceptable factor of safety for
overall global stability is 1.5 under static loading conditions.
Slope stability analyses were performed for east and west slopes of the proposed landfill expansion.
Soil strength and material properties provided in Tables 5-3 were used for the analyses. The
computed minimum factors of safety for circular and block failure surfaces are presented in Table 5-4.
Table 5-4: Results of Slope Stability Analyses
Location Slope
Factor of Safety
Circular Failure Block Failure
East Side 4H:1V 1.8 1.7
West Side 4H:1V 1.9 1.7
© 2017 CDM Smith
All Rights Reserved

2724-105314 02/06/2016
02275-1
SECTION 02275

COMPACTED CLAY LINERS

PART 1 GENERAL

1.01 SCOPE OF WORK

A. Furnish all labor, materials, equipment and incidentals required and install the compacted clay
liner above the subgrade as shown on the Drawings and as specified herein.

1.02 RELATED WORK

A. Section 02200: Landfill Subgrade.

B. Section 02272: Filter Fabric.

C. Section 02274: Geocomposite Drainage Nets.

D. Section 02277: Geosynthetic Clay Liner (GCL).

E. Section 02623: High Density Polyethylene (HDPE) Pipe for Leachate Collection System.

F. Section 02700: Protective Cover Material.

G. Section 02776: Textured High Density Polyethylene (HDPE) Geomembrane.

H. Section 02777: Linear Low Density Polyethylene (LLDPE) Geomembrane Liner.

PART 2 PRODUCT

2.01 MATERIAL

A. Clay liner materials shall conform to the following properties:
· Liquid Limit ASTM D4318 40 minimum
· Plasticity Index ASTM D4318 15 minimum
· Soil Classification ASTM D2487 CH, CL, or MH
· Hydraulic Conductivity ASTM D5084 1.0x10-7 cm/s maximum
· Friction Angle
(Interface with Direct Shear, 15° minimum
Textured HDPE) ASTM D5321