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!1. <br /> <br />4.0 STABILITY ANALYSIS <br />The primary concern of this study is the stability of <br />the proposed waste dump underlain by the thick, relatively <br />loose colluvium/alluvium deposits. These deposits appear to <br />be extensive only within the canyon floor, generally west of <br />boring BH-103. Thus our analysis was concentrated within the <br />1,000-foot western limit of the proposed waste dump. This <br />is generally the area which will receive most of the initial <br />waste dump. We evaluated two basic conditions: the short- <br />term stability during placement of aach fill lift; and the <br />long-term stability after the filling is completed. The <br />critical subsurface conditions are the strength behavior of <br />the soils and the ground water seepage pressures. <br />• <br />In our opinion, the existing canyon soils will exhibit <br />basically a granular strength behavior as related to the final <br />embankme~it load and will not respond as an undrained cohesive • <br />soil. This is a valid assumption due to the limited extent <br />of the fine grain soils, the rate of loading, and the large <br />area loaded by the final embankment. During placement of the <br />L initial few lifts, some areas underlain by sandy silts and <br />clayey silts may e:{hibit local undrained bef~avior. The stabil- <br />ity analyses presented below were performed for various as- <br />I_ sumptions of soil strength parameters. Based on. our limited <br />information, we estimate that the overall effective drained <br />L friction angle of the loose colluvium/alluvium is about 2G° <br />to 300. The undrained shear strength of the soft silt and <br />clayey silt la}~ers within the colluvium/alluvium is probably <br />about 1,000 to 2,000 pcf. <br />'- It is not feasible to accurately predict the final <br />ground water levels after the waste dump is completed. Too <br />-. many key variables such as infiltration rates, changes to <br />area ground water regime due to the mine construction, <br />l <br />~: <br />