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M99012GE <br />5/26/99 <br />Page Two <br />Our stability analysis included performing remolded triaxial <br />compression strength tests of material samples which were remolded <br />to about the same density as the tested sample density of the <br />material encountered in the lower portion of the pile and <br />additional samples remolded to the anticipated density of the <br />anticipated material to be used to construct the remainder of the <br />pile. The differing density data was used to help assess the <br />influence of the low density material in the lower portion of the <br />pile on the overall stability of the pile when completed. <br />Based on our review of the design reports provided by Westec and <br />conversations with Mr. Jim Stover we understand that a subsurface <br />drain system is constructed at the GOB/natural contact interface <br />and the subdrains will continue to be constructed as the pile is <br />constructed. Based on this understanding our stability analysis <br />assumed that the pile would be in a drained condition and would <br />remain in a drained condition throughout the life of the pile. <br />Providing a drained condition of the pile which is necessary to <br />improve the stability of the pile. <br />The stability of any slope is dependent on many factors. Typi- <br />cally the stability of a slope is analyzed by calculating the <br />anticipated gravitational forces that tend to drive the mass of <br />soil downhill and the anticipated internal strength of the soil <br />• along the expected plane of failure that will resist the downhill <br />movements. If the driving forces are equal to or greater than the <br />resisting forces then failure is imminent. A theoretical calculat- <br />ed factor of safety of 1.5 is considered by the geotechnical <br />engineering industry as a minimum factor of safety for a slope to <br />be considered as stable. A calculated factor of safety of 1.0 or <br />less indicates that slope movement is imminent or in process. <br />Failure can occur as slow deformation, creep, or as a somewhat <br />spontaneous failure. <br />Factors that have an adverse influence on slope stability can <br />generally be classified as those that increase the stress (driving <br />force) on the system or decrease the strength (resisting forces) of <br />the soil material. <br />Our stability analyses of the site slope soil material was based <br />on the Bishops Method of Slices. This method is based on the <br />assumption that the slope soil mass will fail in a rotation mode on <br />a circular arc plane. In this method of analysis the mass of soil <br />is divided into many vertical slices. The forces acting on each <br />slice are evaluated from the equilibriurti of the slices; that is, <br />the forces that tend to drive the slice downhill and the forces <br />that tend to resist the movement of the slice. The equilibrium of <br /> <br />Lambert ana associates <br />CO nSULTiRG GE OLEOR NiC~I ERGiR EE RS •RD <br />u~iERU1l }ES~iRG <br />