2006-06-07_PERMIT FILE - C1996083

• Permit No: C1996083
• IBM Index Class Name: Permit File
• Doc Date: 6/7/2006
• Doc Name: 02/15/2006 Gob Pile #2 Stability Evaluation TR-42 Buckhorn Geotech Inc
• Section_Exhibit Name: Volume IX Coal Waste Disposal Area No. 2
• Media Type: D
• Archive: No

southern face of the coal waste stockpile. All inclinometer casing is 2.75 -inch QC casing
manufactured by Slope Indicator, Inc. Inclinometers were generally installed approximately 20
feet into the native foundation soils. The total installed inclinometer depths and depths to native
soils are summarized in Table 3.
Table 3. Summary of Inclinometer Installations
Borehole/
Total
Depth to
Inclinometer
Inclinometer
Native Soil
ID
Depth (ft)
(ft)
BG05 -04
46
28
BG05 -05
56
34
BG05 -07
46
25
A set of baseline readings and the first subsequent quarterly readings have been taken for each
inclinometer. Results to date are discussed in Section 5.2.
4.0 LABORATORY TESTING
Laboratory testing was conducted on in -situ samples obtained during drilling and on bulk
samples collected from the boreholes and from coal waste delivered to the site. Tests performed
include grain size distribution, Atterberg limits, standard proctor, in -situ moisture content and
density, Unconsolidated - Undrained (UU) triaxial compression, and Consolidated- Drained (CU)
triaxial compression with pore pressure measurement. Test results are discussed herein and
presented in Appendices D and E.
4.1 Index Properties
Gradation and Atterberg limits determinations were conducted on three bulk samples of the coal
waste. The samples tested were: GS2, obtained from a depth of 10 to 11.5 feet in BG05 -05,
GS4, obtained from a depth of 10 to 11.5 feet in BG05 -07, and GS5, obtained from a depth of 20
to 21.5 feet in BG05 -07. The samples were found to be composed of approximately 48 to 60%
fines (i.e., silt and clay), 26 to 39% sand, and 9 to 27% gravel. Atterberg limits conducted on the
samples indicated a liquid limit (LL) ranging from 29 to 33, a plastic limit (PL) of 17 to 19, and a
plasticity index (PI) of 12 to 14. Based on these test results the coal waste material classifies as
sandy lean clay (CL) to clayey gravel with sand (GC) according to the Unified Soil
Classification System (USCS).
Specific gravity was determined for four Shelby tube samples of coal waste (SH -04 through SH-
07). The specific gravity of the coal waste material was found to range from 2.15 to 2.49, with
an average specific gravity of 2.35.
Three standard proctor compaction tests have been conducted on coal waste material to date.
The maximum dry density ranges from 85.9 pcf to 104.9 pcf with an average dry density of 93.4
pcf. The optimum moisture content for these tests ranges from 12.7% to 14.9 %.
Bowie No 2 Gob Pile Stability Dec2005
Project #05- 126 -GEO
Page 8 of 18