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1100318 R0T0 0811 JRW1 40 <br />“overshoot” described in Section 5.2.2.2). The effect of fracturing the in- <br />place rock locally results in a decrease in the strength of the un-mined rock <br />exposed at the surface of the quarry. Section 5.3.1.3 discusses how this effect <br />was considered in the material properties used in the slope stability analyses. <br />To study the blasting effect, the material properties were modeled a) as being <br />altered and b) unaltered by blasting. This modeling was achieved by using <br />strength properties selected for unblasted portions of the slope and reduced <br />(blasted) rock strength, respectively. The results of the analysis are contained <br />in Appendix 47. As with over excavation, the effect of the blasting is <br />minimal with an approximately 3-6 percent change in the factor of safety. <br />Therefore, the effect of the blasting is insignificant on the slope stability <br />especially when compared to the substantially greater effects of the clay bed <br />on the slope stability. <br />5.3.3 Cause of the Pikeview Landslide <br />As summarized in the 1994 Amendment, prior slope failures were associated with clay beds in <br />the upper Manitou Formation (Om). The presence of clay beds was reasonably determined not <br />to pose a destabilizing effect for Area H because any beds that may have been present in the <br />upper Manitou Formation (Om) would have been mined and removed prior to commencing <br />quarrying in Area H. Therefore, based on prior experience at the quarry, the design of Area H at <br />the Pikeview Quarry appropriately considered and mitigated a primary source of slope <br />instability, i.e., clay beds, and the reviewing authorities provided approval based on these <br />considerations and mitigation measures provided in the design. <br />As discussed in previous sections, a heretofore unknown clay bed, which extends from the top <br />of the quarry into its base, exists in the Sawatch Formation. As discussed in Section 5.3.2, slope <br />stability analyses indicate that the presence of the clay bed is the single most significant <br />destabilizing condition present in the slope. As discussed in Section 5.3.2, in the absence of the <br />clay bed, the west slope would have been stable with a factor of safety in excess of 4.57 The <br /> <br />57 A slope stability analysis Factor of Safety is a measure of stability of a slope. Factors of Safety less than <br />one (1.0) indicate an unstable slope, i.e., one that will fail. Standard Factor of Safety for slopes used by