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on Hole N was assumed to be representative for this soil type (more so <br />• than Holes J or B). The cohesion, C, as measured was 0.72 ksf (720 psf) <br />and the angle of friction, W, was measured at 30° <br />These results were based on undisturbed satrg~les. The stability analyses <br />were run as prescribed by Von~Unten; a number of searches to produce the <br />lowest calculated factor of safety as measured by Bishop's method of <br />slices. <br />The stability analyses were run under two conditions; phreatic surface and <br />non phreatic. Results indicate that the phreatic condition has the lowest <br />factor of safety (1.56) compared to 1.85 for non phreatic. Both factors <br />are higher than the 1.25 minimum acceptable factor of safety. <br />As an added measure of safety, haul truck drivers will be instructed not <br />to stop along this stretch of the road. <br />Stability at Station 60+00 <br />A similar approach to the stability analysis was used for Sta. 60+00. <br />This section was chosen due to its relative location with respect to <br />unstable ground. This material type was sufficiently different from that <br />of the Hole N area based on landform mapping and therefore strerxYt-h <br />parameters were estimated as being closer to those of Hole B (c = 150 <br />psf) . The ~ was reduced to 30° (from the measured 38°) . Using these <br />parameters should give the laaest factor of safety. A c = 340 psf and ~ <br />= 28° were used for embanlonent material (based on Hole J Triaxial Test). <br />• After the first couple of analyses were conducted, it was evident that <br />due to the failure surface, the haul road had no effect on stability. <br />The haul truck was therefore not added to the section. The lowest factor <br />of safety obtained from both the phreatic and non phreatic analyses was <br />1.34. Please keep in mind the assumed strength parameter used was very <br />low. <br />PREVFN'PATIVE MEASURES <br />As mentioned in John Ivey's report, the unstable areas do not exhibit <br />signs of so called catastrophic failures. The landform does exhibit <br />localized sloughing, some substantial, and hummocky ground. Classic <br />rotational slides have not been observed in this area. The nature of the <br />instability is more reminiscent of creep or slow moving types of failure. <br />In an attempt to stabilize the existing unstable areas, a number of <br />preventative measures can be performed to "head off" a sudden failure, <br />should that ever happen. The stability analyses indicate that the <br />critical areas are, at present, stable. Figure 1S lists considerations <br />in design and construction in unstable areas. <br />Peabody Coal Company has already relocated the road and pond in what <br />Peabody Coal Company considers the "most" stable area and still stay <br />within the confines of the permit area. Unfortunately, the options for <br />further relocation of the road are limited at best. The coal has to be <br />hauled from the North Mining Block by way of this particular route. <br />Minor adjustments can and will be made to the alignment, especially in <br />5 <br />