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• majority of the clay soils below the pile are very stiff (unconfined strengths <br /> <br /> <br />on the order of 5,000 to 8,000 psf) and are partially saturated. The total <br />stress strength parameters measured in the CU test are considered to be <br />very conservative values for the overall clay soil strength. Even after <br />compression under the full pile height, we do not believe the clay will be <br />saturated. Based upon the unconfined strength values and partial saturation <br />of the clay we believe values on the order of ~ = 25 degrees and cohesion <br />= 1500 psf represent a conservative, but more realistic estimate of the clay <br />strength for total stress conditions. <br />Moist unit weights determined from drive samples in the clay ranged <br />from 120 to 130 pcf (Table B-I). Properties for the clay used in the stability <br /> <br />• analysis were: <br />Undrained -Normal Value m = 25 degrees, Cohesion = 380 psf <br />Shear Strength -Lower Bound ~ = 20 degrees, Cohesion = 250 psf <br /> <br />Total Stress -Normal Value ~ = 25 degrees, Cohesion = 1500 psf <br />Shear Strength -Lower Bound ~ = 15 degrees, Cohesion = 750 psf <br />Unit Weight -Normal Value = 120 pcf, Lower Bound 100 pcf <br /> <br />• <br />• <br />Spoil. CTL/Thompson, Inc. performed several previous investigations <br />of spoil pile properties at this site and other nearby coal mines which involved <br />very similar bedrock formations, spoil materials and mining methods <br />(References 2 through 9). These previous studies included direct shear <br />testing, measurement of angles of repose, and large scale sand cone and <br />nuclear density testing. Previously measured angles of repose varied from <br />• 34 to 40 degrees. Previous direct shear test results showed friction angles <br />12 <br /> <br />