2006-06-07_PERMIT FILE - C1996083

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Pill A-11 L 1.6 m u C m CL 14 tmn 1 2 `o 0 1.0 LL 08 0.6 4— 500 Figure 2. Sensitivity Plot for 4H:1V Slope 700 900 1100 1300 1500 1700 1900 2100 2300 2500 Undrained Shear Strength (Gob) (lb/N2) 6.2 Long -Term Analyses Long -term stability analyses assume that pore pressures are in equilibrium with the stress conditions. In other words, pore pressures are not in excess of hydrostatic or steady -state seepage. This may occur at completion of fill placement or years after fill placement. For these analyses, effective stress shear strength parameters (Table 7), drained conditions, and an assumed water table were used. The depth to the water table was varied to determine the sensitivity to the factor of safety. While many analyses were conducted, critical results are presented in Table 9. Table 9. Summary of Long -Term (Drained) Analyses Notes: 1. Overall angle for slopes above lower bench (i.e., above bottom 50 vertical feet) 2. Factor of safety according to Spencer's procedure For most analyses, the factor of safety for long -term drained conditions was found to be 1.5 or greater. As indicated in the table above the exception is for a 3H:1 V slope with an assumed high water table, indicating a factor of safety of 1.27. This emphasizes the sensitivity to the location of the water table for long -term stability. Factors of safety with respect to stability greater than 1.5 are considered to be acceptable for long -term conditions. However, the excess pore pressures and short -term analyses should dictate Bowie No 2 Gob Pile Stability Dec2005 Project #05- 126 -GEO Page 16 of 18 Factor of Slope' Description Safetv2 5H:1V High water table 1.74 Critical failure at lower bench 4H:1 V High water table 1.64 Critical failure is deep into native soils 3H:1 V Moderate depth to water table 1.53 3H:1 V High water table 1.29 Notes: 1. Overall angle for slopes above lower bench (i.e., above bottom 50 vertical feet) 2. Factor of safety according to Spencer's procedure For most analyses, the factor of safety for long -term drained conditions was found to be 1.5 or greater. As indicated in the table above the exception is for a 3H:1 V slope with an assumed high water table, indicating a factor of safety of 1.27. This emphasizes the sensitivity to the location of the water table for long -term stability. Factors of safety with respect to stability greater than 1.5 are considered to be acceptable for long -term conditions. However, the excess pore pressures and short -term analyses should dictate Bowie No 2 Gob Pile Stability Dec2005 Project #05- 126 -GEO Page 16 of 18