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0 <br />• Effective Stress k7 = 25', C = 500 psf <br />Total Stress P1= 15', C = 750 psf <br />Unit Weight y = 125 pcf <br />Spoil strength and density is difficult to measure in laboratory or field tests <br />due to the large particle sizes. The angle of repose is considered a good indicator <br />of friction angle. Our experience and technical review indicated a friction angle of <br />34 degrees with no cohesion (total or effective), and a unit weight of 100 pcf are <br />conservative but realistic values. <br />RESULTS OF STABILITY ANALYSIS <br />The stability analyses were performed using the simplified Bishop method. <br />Normal parameters were selected for strength and density. For this condition <br />factors of safety of 1.6 (total stress, construction phase) and 1.9 to 2.0 effective <br />stress, long term) were calculated. <br />• <br />The effects of water buildup within the fill were evaluated by simulating water <br />buildup to two levels as shown on Fig. A•I. The worst case water conditions <br />(extending to the toe) show low factors of safety for slump failures near the toe (1.3 <br />to 1.4). This is expected and indicates that drainage and control of subsurface water <br />are critical near the toe. The less severe water conditions (water buildup limited to <br />back 3/4 of fill) indicate factors of safety on the order of 1.5 to 1.8. Although these <br />may be considered adequate, sutable drainage through this zone is still considered <br />necessary. <br />The factor of safety is not particularly sensitive to variations in spoil unit <br />weight. The models are sensitive to the clay friction and cohesion values. As shown <br />on Fig. A-2 the factor of safety drops rapidly, particularly with respects to the friction <br />of the clay layer. Based upon our experience and the information available at this <br />time, we believe suitable strength values will likely be found in the residual/colluvial <br />• clays anticipated over most of fill sites. Softer/looser soils may require removal in <br />LORENOITO COAL COMPANY <br />CM 35,251 9 <br />