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M99012GE <br />5/26/99 <br />Page Four <br />In our stability analysis we varied the soil strength values from <br />those listed above to assess the sensitivity of the analysis to <br />varying soil strength parameters. The variations in our analysis <br />produced relatively small and predictable changes to the calculated <br />theoretical factor of safety calculated indicating that the stabil- <br />ity analysis was not sensitive to slight variances in the soil <br />strength characteristics. The stability analysis of the cross <br />section provided by Jim Stover indicated a theoretical calculated <br />static factor of safety greater than 1.5. The results of our <br />stability analysis are presented on Figures 1 through 6. <br />Our stability analysis is based on the subdrains installed and <br />working resulting in an assumed drained condition as discussed <br />above. If the GOB pile should become undrained, partially <br />saturated or saturated, the theoretical calculated factor of safety <br />may be much lower than that calculated for a drained condition. <br />Our stability analysis is based on the assumptions of an intimate <br />and competent contact between the GOB fill material and the natural <br />support material which include the organic topsoil removed and the <br />exposed surface of the natural foundation support soil materials <br />benched prior to placement of the GOB material. <br />The benching of the natural foundation support soil materials to <br />expose competent support material reduces the potential for <br />developing a predetermined failure plane along the GOB/natural <br />material contact. We suggest that future plans include benching <br />into the natural material to receive the fill material prior to <br />placing additional GOB material. The benching should continue into <br />competent foundation support material as the GOB material is placed <br />as the pile height is increased. The benching concept is shown on <br />Figure 7. <br />We suggest that as the GOB pile is extended in height the planned <br />drain system continue with the construction to provide subsurface <br />drainage throughout the entire pile. <br />i <br />~l.ambcrt ana ~,s~aciates <br />CONSUL9NG GEOTECN N~L~L ENGwEE RS •ND <br />MAtE RILL TESTING <br />