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• <br />-21- <br />contents near its plastic limit. Information published by Energy Mines and <br />Resources Canada ( Canmet) in "Pit Slope Manual" suggests that similar cohesive <br />soils have coehsion between 500 and 1,000 psf and internal friction angles <br />less than 10 degrees. The ranges of strength published in Canmet are consistent <br />with those we have generally obtained from previous testing of cohesive ma- <br />terials at the Eckman Park facility. During our analysis, we varied strengths <br />of the fire clay between C =500 and 1,000 psf and 0=0 to 10 degrees to evaluate <br />the affect the material has on mass stability. <br />Seepage was noted at the toe of the spoil throughout much of the pit. <br />Ground water appears to be moving downdip along the old pit floor as a result <br />of surface infiltration. Our analysis considered that ground water was moving <br />along the pit floor about 1 foot above the bedrock surface. A second condition <br />• <br />considered that the phreat1c surface was 20 feet above the pit floor. In <br />our opinion, the first ground water condition is the more likely for the pit <br />in general considering the materials are highly permeable and moving downdip <br />at about a 10 percent grade. The second case was used to simulate the presence <br />of a barrier or zone of low permeability materials within the spoil which <br />causes transient water to pool. <br />Analysis Methods <br />Several methods of analysis were utilized in evaluating stability <br />of the spoil. One procedure considered circular failure surfaces which <br />were analyzed using the simplified Bishop method. A similar method of <br />analysis that considers non - circular or planar failure surfaces is based <br />upon the modified Spencer method. Both of these methods divide the area <br />• <br />above the failure surface into several vertical segments and consider <br />