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• ~ <br />' United Companies, Inc. <br />March 2f, 1994 <br />Page 5 <br />' equal to the angle of repose produces a safely Pactor ranging from <br />1.15 to 1.54 with the range of arnllas presented. <br />1 <br />Cohesionless soil slopes do not fail in rotational type failures <br />' but in slough or wedge type failure where the angle of the cut <br />slope declines to near the angle of repose. A wedge type stability <br />' analysis was run using a 1:1 slope to a 1.5:1 (horizontal to <br />vertical) slope. A safety factor oP 1.26 was determined for these <br />parameters and with no seismic acceleration. The gravel pit <br />extension is in a seismic zone one which is a low potential <br />earthquake zone. Seismic acceleration is generally assumed to be <br />between 0.10 and 0.20. California uses a value of 0.25 where <br />earthquake potential fa high and the intensity of the earthquakes <br />' are large. Nith a seismic acceleration value of o. 1o the above <br />fliscussed wedge has a safety factor of I.14. The safety factor is <br />' above unity and Ss adequate for the temporary elope. Using <br />Californians much morn intense value of acceleration the factor of <br />' safety would be 0.87 which is less than unity. This would indicate <br />some sloughing or wedge type failure would occur to decrease the <br />' elope angle. A 2:1 slope was analyzed with the more intense <br />acceleration value (0.25) with a 1.08 safely factor detarmined~. An <br />' intense earthquake is not expected and has not occurred since <br />records have been kept of the area. <br />' Numerous soil experts, including the Bureau of Reclamation in their <br />Earth Nanual, recommend axcavat~ slopes Por this type operation to <br />' be 1:1 on a standard basis. some small sloughing ie expected to <br />occur with time due to vibration or wetting from rainfall or snow <br />anfl from frost heave. These samn sources recommend 1.5:1 elopes for <br />permanent borrow pit and reservoir area back alopea. However, they <br />do recommend tits elope be increased where the public hea access. <br />Ths pit will be excavated to or near to the elevation of the east <br />aide of the property. No water will be encountered thus, no <br /> <br />Colons Pit November 06 S-9 <br />