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47 <br />many of the larger grain sizes would break down during placement and <br />compaction of the waste material. This would result in a more sand -like granular <br />deposit. <br />Since extensive testing would not be conducted until representative refuse <br />material was generated by the plant, the density and strength of the spoil material <br />was estimated using Bureau of Mines Report of Investigation 796 titled "Physical <br />Property Data on Coal Waste Embankment Materials". By averaging data from <br />seven similar waste sites presented in this report, the parameters presented below <br />were selected for use in this analysis. <br />Selected Material Parameters <br />Parameter Selected Value <br />In-place density (psf) <br />Dry, yd. 90 pcf <br />Wet, yw 104 pcf <br />Angle of internal friction, 0/ 33.4 degrees <br />Cohesion, c(psf) 446 psf <br />As mentioned, consolidated materials underlie the majority of the area. Strata of <br />this nature are relatively strong and not subject to differential settlement from the <br />loads placed upon it by the waste pile. Because of this, the internal integrity of the <br />proposed homogeneous pile is the major concern with regard to the operational <br />stability of the embankment. It is expected that the critical areas for failure will <br />occur within the pile itself, and not through the foundation strata. In the analysis, <br />the foundation strata were given a high strength value, so that the failure would <br />occur through the pile. <br />Stability analyses in this report used a computerized stability program called <br />STBL2. STBL2 uses a modification of the simplified Bishop method of slices in <br />which overall horizontal force equilibrium is satisfied instead of overall moment <br />equilibrium. In this manner, it is capable of analyzing both circular and non - <br />circular failure surfaces. This method is also known as Janbu's simplified <br />procedure, which is the same expression as that derived, by Carter (Siegel, 1975). <br />STBL2 has a routine which searches 100 circular failure surfaces for the most <br />critical sections and a routine to calculate the safety factor for any designated <br />non -circular failure surface. <br />Initially, a potential failure plane along the interface between the pile and <br />foundation strata was analyzed for stability. To supplement this, a random circle <br />searching routine was used to find the critical circle within the pile. As <br />mentioned, the channel is a drainage way for an ephemeral stream. Since all <br />surface water will be diverted from the pile itself, excessive positive water <br />pressures are not likely to develop within the pile (Wardwell 1982). Because of <br />Section 2.05 RN -6 10/17/2016 <br />