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-16- <br />• methods yield a more conservative factor of safety. The impact of <br />the other variables is much greater than the method of mathematical <br />analysis. Most of the effort in this investigation has been in <br />the direction of defining as well as possible the critical strength <br />parameters for evaluation of the fill and the foundation conditions. <br />Foundation Conditions <br />Foundation conditions in the various areas were discussed under <br />both 'Geologic Conditions' and 'Foundation Conditions'. To reit- <br />erate, these general conditions consist of a thin layer of clay <br />soils which range from stiff to soft, underlain by relatively com- <br />petent sedimentary bedrock. Relatively soft clays indicate the <br />• foundation conditions may control the rate of placement and the type <br />of failure most likely for these disposal areas. The soft to medium <br />stiff clays were observed to have a cohesion of L000 psf and ~ = 0. <br />This represents an undrained shear strength. The strength of these <br />clays should increase with time as consolidation occurs. For pur- <br />poses of analysis, the stiff clay layer was assumed to have shear <br />strength of 2,000 psf and a friction angle of 15 degrees. The under- <br />lying bedrock was assumed to have a cohesion intercept of 5,000 psf <br />and a friction angle of 15 degrees. <br />Characteristics of Fill <br />The characteristics of the fill material were estimated from <br />observation of the performance of the existing spoil piles associ- <br />• ated with the present mining, results of laboratory classification <br />