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Case 8-3 —The resulting safety factors of 2.21 (static) and 1.77 (pseudo-static) during a <br /> rapid drawdown condition exceed the minimum required MLRB safety factors of 1.5 <br /> (static) and 1.3 (pseudo-static) for critical structures. The resulting safety factors of 3.79 <br /> (static) and 2.70 (pseudo-static) during a full reservoir condition also exceed the <br /> minimum required MLRB safety factors for critical structures. The proposed setback of <br /> 75 feet from the edge of road is satisfactory. <br /> Case 8-4—The resulting safety factors of 1.59 (static) and 1.33 (pseudo-static) during a <br /> rapid drawdown condition exceed the minimum required MLRB safety factors of 1.3 <br /> (static) and 1.15 (pseudo-static)for non-critical structures. The resulting safety factors of <br /> 2.82 (static) and 2.14 (pseudo-static) during a full reservoir condition also exceed the <br /> minimum required MLRB safety factors for non-critical structures. The proposed setback <br /> of 50 feet from the edge of the highway parcel is satisfactory. <br /> The following recommendations for monitoring of slope stability should be followed: <br /> 1. A visual inspection of the excavated slopes should be done on a weekly basis for <br /> the duration of mining. This inspection should consist of walking the existing <br /> ground and looking for any signs of stress cracks or other potential signs of slope <br /> failure. Some minor sloughing of slopes is expected on any mine site. The intent <br /> of this inspection is to locate potential major slope failures that could potentially <br /> extend back into a structure. <br /> 2. A visual inspection should be done after a major precipitation event that has <br /> saturated the ground using the same procedures. A major precipitation event <br /> would be defined as a storm that produces an intensity level reached once in 50 <br /> years on the average. <br /> 3. If a visual inspection detects signs of a potential slope failure, qualified personnel <br /> should be contacted to evaluate and recommend remediation work to stabilize <br /> the area. <br /> 4. If no visible signs of slope failure are detected during mining, then the inspection <br /> period could be reduced to once per 6 months after mining completion, or after <br /> every major precipitation event. <br /> West Farm Gravel Pit Expansion <br /> 7 Slope Stability Analysis <br /> r Page 9 <br />