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materials. In these cases, the shear strength assumptions utilized in the foundation area had little or no effect on the factor of safety. In the case of one condition analyzed (that condition dealing with the backfill of the portal area only to the existing bench level in the high wall cut above the portal, and the use of on-site borrow material from the existing bench fill) the shear strength assumptions were found to have a marked effect on results of the analysis. The three different factc•rs of safety obtained for the different assump- tions of shear strength have been plotted and will be found on a graph in the Appendix of this report. This plot indicates that the minimum required factor of safety of 1.3 required for this project can be satisfied if the foundation materials are assumed to have a friction angle of 91 degrees or more. A 41 degree friction angle would, in our opinion, not be at all unrealistic for a material of the nature and density condition observed on this site. More specific information on the result of analyses will be found later in this report. With respect to the existing bench fill materials at the west portal area, the residual effective stress shear strength values were utilized for these materials. The higher Peak effective stress shear strength data was used to model any additional fill materials which will be placed above the existing bench fill, and used to cover the portal area. It is assumed that this material will be compacted to a minimum of 95$ of Standard Proctor Density, ASTM D-698. Visual examination at the base of the existing bench fill area indicates a layer on the order of 12-feet in thickness, rich in boulder and cobble size rock fragments. This layer would be associated with a somewhat higher shear strength than the overlying silt and clay-rich 1 fill m<terials. From past experience, such materials have been 1 -~-