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<br />• 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. liowever, 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 invesl:igated 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 C~ile 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 levers as described above (in cross-section 4, the <br />50-year flood elevation is 6,615.6 feet while ground watE~r above the <br />colluvium is assumed at elevation 6,622 feet). The assumpti~m of ground <br />water 5 feet above the colluvium are therefore more conservative than <br />• <br />21 <br />