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A shallow or sliver-type surficial sliding is represented by a <br /> failure surface that is located at a shallow depth and extends from the <br /> toe to slightly behind the crest of the pile. This is always the critical <br /> case for a cohesionless material on a strong foundation. However, the <br /> volume of material which would be involved in a failure of this type is <br /> small and the consequences of such failure are typically not severe. <br /> Deeper failures within the waste could involve large volumes of <br /> waste and could therefore have much more serious consequences. These have <br /> been represented by assuming a failure surface located slightly above the <br /> base of the waste rock. <br /> Foundation failures are represented by assuming a failure surface <br /> which passes through the colluvial soils underlying the waste rock. <br /> All stability analyses were initially run assuming dry (fully <br /> drained) conditions. In view of the free-draining character of the waste <br /> rock , this is considered to be the condition which will generally occur <br /> within the piles. However, an additional case was investigated that <br /> assumed ground water occurring within the waste pile material ; for such a <br /> case it was assumed that a piezometric surface would lie approximately 5 <br /> feet above the base of the pile. Such a case investigates the possibility <br /> of ground water above the colluvial soils underlying the pile and the <br /> saturation of the lower 5 feet of the waste pile material . In view of <br /> the nature of the waste rock, this is considered to be a very conserva- <br /> tive assumption of ground water conditions. <br /> Results of the surface hydrologic analyses and hydraulic studies <br /> presented in Section 5.0 of this report indicate that the maximum elevation <br /> of flood waters in Ralston Creek for the design 50-year event is below <br /> the ground water levels as described above (in cross-section 4, the <br /> 50-year flood elevation is 6,615.6 feet while ground water above the <br /> colluvium is assumed at elevation 6,622 feet) . The assumption of ground <br /> water 5 feet above the colluvium are therefore more conservative than <br /> '1 <br />