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5.2.2 Foundation Soils <br />Sheaz strength pazameters for the foundation soils were estimated based on UU and CU triaxial <br />compression tests as summarized in Tables 5 and 7. Mohr-Coulomb failure criteria (~ and c) <br />were used to model the strength of the foundation soils. The same criteria were used for total <br />and effective stress stability analyses. A total stress failure envelope (~=30° and c=0) was <br />developed based on total stress path plots from UU triaxial tests conducted at various confining <br />pressures. These stress path analyses aze included with the triaxial test data presented in <br />Appendix C. These total stress failure criteria aze considered a conservative estimate of effective <br />stress strength parameters when compazed to results of the CU triaxial test conducted on a <br />sample of the foundation soil. Due to the limited CU triaxial tests and associated uncertainty of <br />the effective stress strength pazameters, the same strength pazameters were used for the <br />foundation soils for total and effective stress analyses. The moist unit weight of native soils was <br />assumed to be 125 pcf for the stability model. <br />Table 8. Strength Parameters Used in the Stability Evaluations <br /> Foundation Soils Gob <br /> Undrained <br /> Shear Strength, - 1578 psf <br />Total Stress Su <br />Analyses ~ (deg) 30 - <br /> c (psfl o -- <br />ENedive ~' (deg) 30 31 <br />• <br />Stress <br />Anayses C~(p5fl 0 0 <br />5.3 Stability Evaluation Results <br />Factors of safety from critical failure surfaces for each cross-section aze summarized in Table 9. <br />Output from these critical stability analyses is presented in Appendix E. The slopes and total <br />height of the gob pile were optimized in order to achieve a minimum factor of safety of 1.50 for <br />both total and effective stress analyses. As indicated in Table 9, four gob geometries and heights <br />result in a factor of safety of at least 1.50: <br />- 2.SH:1 V gob slopes to a maximum gob height of 95 vertical feet <br />- 2.H:1 V gob slopes from 0-50 feet and 3H:1 V from 50 to 105 feet (ultimate height) <br />- 2.SH:1 V gob slopes from 0-50 feet and 3.SH:1 V from 50 to 110 feet (ultimate height) <br />- 3H:1 V gob slopes to a maximum gob height of 115 feet <br />As noted in Table 9 and in Appendix E, the ultimate gob pile height discussed in this report is <br />measured from the down slope toe of the wastepile to the top of the pile. <br />• <br />Bowie Gob Pile No. 3 stability report <br />Project #06-0g1-002 <br />Page I3 of 17 <br />