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advanced to depths of 41.5 to 46.5 feet. No native foundation soils or bedrock was encountered <br />in any of the boreholes. No groundwater was encountered during or immediately after drilling, <br />however, no piezometers were installed. Eight Shelby tube samples were obtained from the <br />three boreholes for strength testing. Laboratory testing conducted on these samples is discussed <br />in Section 4.0. <br />4.0 LABORATORY TESTING <br />Laboratory testing was conducted on bulk and "undisturbed" samples obtained during drilling at <br />the Gob Pile No. 3 foundation and in compacted gob at the existing Gob Pile No. 2. Tests <br />performed include grain size distribution, Atterberg limits, in-situ moisture content and density, <br />swell-consolidation, Unconsolidated-Undrained (UU) triaxial compression, and Consolidated- <br />Drained (CU) triaxial compression with pore pressure measurement. Test results are discussed <br />herein and presented in Appendices B, C, and D. <br />4.1 Index Properties <br />Index testing was conducted on samples of foundation soils at the Gob Pile No. 3 footprint. <br />These results are summarized in Table 3 and presented in Appendix B. Index testing has been <br />previously conducted on gob material from Gob Pite No. 2. These results are discussed by <br />Buckhorn Geotech (2006). <br />• Gradation and Atterberg limits determinations were conducted on eight bulk samples of <br />foundation soils at Gob Pile No. 3. The samples were determined to be composed of 26 to 87% <br />fines (i.e., silt and clay), 8 to 43% sand, and 0 to 42% gravel. It is important to note that due to <br />the relatively small split spoon sample size and diameter, the coarse soil fraction (e.g., cobbles <br />and boulder content) are not represented in these results. The plasticity index (PI) of these same <br />soils ranged from 4 to 21, with an average PI of 12. Based on these test results, the samples <br />classify as lean clay with variable gravel (CL) to clayey sand (SC) to clayey or silty gravel (GC <br />or GM). Natural moisture content of these samples ranged from 6.9 to 15.9%. <br />Four swell consolidation were conducted on samples obtained of foundation soils at Gob Pile <br />No. 3. The samples exhibited low swell-potential to moderate collapse potential. Moderate to <br />high potential for consolidation was observed in the tests, indicating that moderate settlement <br />should be expected for the gob pile. <br /> <br />Bowie Gob Pile No. 3 stability report <br />Project N06-481-002 <br />Page 7 of 17 <br />