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• We used a conservative strength value similar to a very sandy clay for this layer. A <br />friction angle of 25 degrees, cohesion of 500 psf and moist unit weight of 12o pcf <br />were selected as normal parameters. <br />Bedrock. The bedrock consists of hard to very hard interbedded sandstone <br />and sandy shale. We do not believe that a failure through the bedrock layer is likely <br />due to the high strength of the layer. The regional dip of the bedrock is 4 to 5 <br />degree to the north-northeast which is in a favorable direction with regard to the <br />RDA. For the bedrock a friction angle of 25 degrees, a cohesion of 5,000 psf and <br />a unit weight of 125 pcf were used. These values were sufficient so that critical <br />surfaces did not pass through the bedrock layer and the properties were not varied <br />in the analysis. <br />Water Conditions. Five water conditions within the RDA were considered. <br />• The water level conditions are shown on Fig. 6 and are described as follows: <br />1. A 10-foot thick saturated layer at the base of the RDA. <br />2. A 20-foot thick saturated layer at the base of the RDA. <br />3. A 50-foot thick saturated layer between Benches 3 and 4. <br />4. A varying water level from 10-feet thick at the toe of the RDA, <br />increasing uniformly to 1/4 the pile height at the crest. <br />5. A varying water level from 10-feet thick at the toe of the RDA, <br />increasing uniformly to 1!2 the pile height at the crest. <br />The water conditions evaluated were intentionally increased in severity until <br />the calculated factors of safety were low. Conditions 1 through 3 are considered <br />reasonable possibilities. Conditions 4 and 5 were evaluated as worst case <br />conditions but are not considered likely. The results of the current investigation did <br />not indicate a significant build up of water at the base of the RDA in the borings <br />• <br />19 <br />