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As can be seen from worksheet 2 , a net volume of nearly 26, 000 <br /> cubic yards is available between stations 1 and station 10. <br /> Approximately 5000 cubic yards is already in place resulting in a <br /> total volume of 31, 000 cubic yards which exceeds the required <br /> 30, 000 cubic yards. If, in the future, the estimate of mine waste <br /> is revised to exceed this value the pile will be extended further <br /> up the valley. <br /> Stability Analysis <br /> A limit equilibrium analysis for plane surfaces, similar to that <br /> presented by Huang (1983) was used to assess the stability of the <br /> design configuration. The analysis is appropriate for simple <br /> geometries with plane failure surfaces. The fill geometry at <br /> sections 1-10 is assumed to be triangular as shown in figure 4 . <br /> Because of the very shallow depth to bedrock a circular failure <br /> plane is very unlikely and a plane failure surface parallel to the <br /> bedrock is expected. Static equilibrium equations were derived for <br /> the specific triangular geometry occurring at this site. The free <br /> body diagram for this case is shown in figure 4 . Derivation of the <br /> stability equations are included in the appendix. <br /> The limit equilibrium analysis results in a quadratic expression <br /> for the factor of safety which is a function of several parameters; <br /> a - back slope <br /> c - cohesion coefficient <br /> 0 - friction angle <br /> ru - pore water ratio <br /> Wi - weight of the block <br /> Li - length of the block foundation interface <br /> The geometry parameters, a, Wi and L, were measure from the cross <br /> sections. The pore water ratio was assumed to be ru = 0.25, which <br /> means that ', of the fill is saturated. This is very unlikely but <br /> again is used to assure a conservative design. <br /> A numeric trial and error technique was used to solve the <br /> quadratic for the factor of safety. The results are shown on <br /> worksheet 3 . The stability analysis was completed for two sections. <br /> Section 5 is the most critical section because of it large size, <br /> and hence weight. Section 8 is the smallest section, excluding <br /> section 1. Section 5 resulted in factor of safety of 1.85 and <br /> sections 8 a factor of safety of 2 .74 . Each of these is well above <br /> the required factor of safety of 1.5 and they should bracket the <br /> factors of safety for all other sections. <br /> 7 <br />