2018-10-12_REVISION - C1982056 ‎(2)‎

• Permit No: C1982056
• IBM Index Class Name: Revision
• Doc Date: 10/12/2018
• Doc Name: Correspondence
• From: Twentymile Coal, LLC
• To: DRMS
• Type & Sequence: TR84
• Email Name: TNL
• Media Type: D
• Archive: No

Vine Laboratories, Inc. (Denver, CO) performed laboratory testing on select samples collected from the
investigation to quantify soil properties. The laboratory testing results are included in Appendix F, and
summarized in Table 5 below.
Index testing and soils gradations confirmed visual classifications of the on-site soils according to the Unified
Soil Classification System (USCS) with fines contents typically exceeding 80 percent, as shown in Figures 3-2
and 3-3. Previous test data from the 2007 Site Investigation for the 6MN pond are also shown for reference.
70
p Previous Data
60
• 2016 Testpits
x so
40
T
'u
30
a
20
ao
10 p ML
0
0 20 40 60
Liquid Limit
Figure 3-2: Plasticity Chart Depicting Distribution of Atterberg Limits from Laboratory Tests
S15
1n
v
06
E
M
4- 10
0
CP
E
0 5
Z
0
® 2016 Testpits
■ Previous Data
0 5 612 1324 2537 38-50 5180 81 100
Fines Content {t)
Figu re 3-3: Distribution of Fines Content from Sieve Testing of Samples
3.2 Geotechnical Stability Analysis
Stability analyses of the embankment slopes were conducted to ensure that the global stability of the
embankments met the minimum design criteria. Three loading conditions were considered during the
stability analysis: End -of -Construction, Steady -State Seepage and Pseudostatic Seismic Analyses.
Slope stability analyses were performed using Slide, Version 7 (Rocscience, 2016). Limit equilibrium
calculations are made to compute factors of safety with critical failure surfaces are identified using
optimization search methods without constraints on the slip surface shape or location. A 3H:1V slope, the
PEABODY -FINAL-DESIGN-:FM-20181010 3-3
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