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SHANNON t~ WILSON, iNC. <br />• <br />6.2.1 Spoil <br />The spoil will consist of excavated bedrock composed of sandstone, siltstone and <br />mudstone. Gradational characteristics of spoil in the West Pit were evaluated in Reference 7. <br />The relatively high lift thicknesses, 30 to 100 feet, and end dumping over the edge of the lift <br />produce significant sorting of the spoil. Very course (D50 of 10 inches) spoil is typically present <br />at the base of the lifts. Unsorted spoil was estimated to have the following gradational <br />characteristics (Reference 8}. <br />Cobbles and boulders 50% <br />Gravel 28% <br />Sand 2% <br />Fines (-#200 sieve) 20% <br /> <br />The spoil material has steep angles of repose on the order of 38 or more degrees. We <br />modeled the spoil as a cohesionless material with a friction angle of 30 degrees. A density of <br />100 pcf was assumed. For the parametric analysis of the valley £11, the friction angle was varied <br />from 25 to 35 degrees and the unit weight varied from 90 to 120 pcf. <br />6.2.2 Overburden Soils <br /> <br />The overburden soils typically consisted of gravel-sized bedrock fragments within a <br />clayey or sandy matrix. Gradation testing showed about 50 to 70 percent low plasticity fines <br />with 30 to 40 percent sand and about 10 percent gravel (Figures B-1, B-2 and Table B-1). Direct <br />shear tests were performed on intact liner samples obtained in boring ST-1 (Figures B-3) during <br />the current study. Shear strength tests were typically performed at a maximum normal force of <br />4,000 psf, and the strength envelope was extrapolated to higher levels below deeper fills. <br />Flattening of the envelope at higher normal forces is expected, but not easily quantified. It is our <br />opinion that this is balanced by other conservative assumptions, such as ignoring three- <br />dimensional effects in a confining valley and assuming that weak clay layers are present and <br />continuous beneath the entire fill. <br />In addition, we reviewed direct shear tests and consolidated-undrained (CU) tests <br />performed on intact and remolded samples during previous studies by others. A summary of <br />overburden strength test results for the current and previous studies is shown on Figure 7. <br />23-1-01105-200-Rl.doc <br />23-1-01105-200 <br />