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• however, no piezometers were installed. Pore pressures are currently being monitored at Gob <br />Pile No. 2 with vibrating wire piezometers installed during a previous investigation (Buckhorn, <br />2006). Eight Shelby tube samples were obtained from the three boreholes. Laboratory testing <br />on these samples is discussed in Section 4.0. <br />4.0 LABORATORY TESTING <br />Laboratory testing was conducted on thin-walled samples of gob obtained during drilling at Gob <br />Pile No. 2 and on bulk samples collected from boreholes drilled at the Gob Pile No. 4 <br />foundation. Tests performed include natural moisture content, grain size distribution, Atterberg <br />limits, and unconsolidated-undrained (UU) triaxial shear. Consolidated-undrained (CU) triaxial <br />shear were conducted previously as part of our evaluation of Gob Pile No. 2. These CU triaxial <br />shear results were used for the stability evaluation of Gob Pile No. 4. Test results, including <br />those previously conducted, are discussed in this section and presented in Appendices C and D. <br />4.1 Index Properties <br />Gradation and Atterberg limits deternunations were conducted on five bulk samples of the <br />foundation soils obtained during drilling at Gob Pile No. 4. The samples were mostly collected <br />with standard split spoon samplers. Consequently, the sample sizes were limited and may not be <br />completely representative. Nonetheless, the samples were found to be composed of <br />approximately 29 to 66% fines (i.e., silt and clay), 22 to 44% sand, and 5 to 27% gravel. <br />Atterberg limits conducted on the samples indicated liquid limits (LL) ranging from 24 to 34, <br />plastic limits (PL) of 14 to 18, and plasticity indices (PI) of 9 to 19. Based on these test results <br />the foundation soils classify as sandy lean clay (CL) to clayey sand (SC) according to the Unified <br />Soil Classification System (USCS). It should be emphasized that considerable gravel, cobble <br />and boulder content is not represented in the samples. Foundation soils more likely classify as <br />clayey gravel (GC) to gravelly lean clay (CL). Index test results are summarized in Table 2. <br />Table 2. Summary of Index Testing <br /> In-Situ <br /> Sample Moisture Atterberg Sieve Anal sis <br />Borehole Sample Depth Content Limits <br />ID ID ft % LL PL PI Gravel Sand Fines USCS <br />BGO6-O6 GS45 10-11 7.8 24 15 9 27 44 29 SC <br /> GS46 25-26 10.1 26 14 14 5 35 60 CL <br /> BS1 Surface 15.6 33 18 15 12 22 66 CL <br />BG06-09 GS48 15-16 9.7 30 17 13 17 42 41 SC <br /> GS60 35 11.9 34 15 19 6 44 50 CL <br />NOTES: <br />LL =LIQUID LIMIT <br />PL =PLASTIC LIMIT <br />PI =PLASTICITY INDEX <br />NP = NON-PLASTIC <br />USCS = UNIFIED SOIL CLASSIFICATION SYSTEM <br />Bowie Gob Pile No. 4 stability report <br />Project #OS-126-GEO <br />Page 8 of IS <br />