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1 <br /> <br /> <br />1 <br /> <br /> <br />1 <br />1 <br /> <br />suggest that some of the water in the northern portion of the pile <br />may originate at the pile perimeter, or away from the pile. From <br />an examination of the original foundation topography an existing <br />streambed (entering the footprint along the northern perimeter) is <br />covered by the pile. The old streambed could represent a pervious <br />zone which allows ready access of outside moisture into the <br />foundation alluvium. We understand that some offsite surface <br />seepage persists along the northern pile/foundation contact area. <br />Considering the foregoing discussion two single line <br />piezometric surfaces were modelled for the third and final critical <br />stability section (Section C-C shown on Plate 1). The first <br />considers a piezometric level based on available data only and is <br />presented on Plate 11 of the Appendix. The second surface emulates <br />a dome or cone of pore pressure which intercepts the slope surface <br />at the first slope bench and assumes to contain suspected aquifers <br />within the pile. Because the extent of suspected aquifers or <br />impervious boundaries is completely unknown, this surface begins at <br />the contact between the alluvium and the pile on the upper or east <br />slope; intercepts PZ B2-2 at elevation 4544.5; rises to the ground <br />surface at PZ P-1; and finally drops to the tip elevation of PZ <br />BO-2. The critical section depicting the piezometric surface thus <br />described, is presented as Plate 12 of the Appendix. <br />STABILITY ANALYSIS RESULTS: <br />1 <br /> <br /> <br />1 <br />1 <br />1 <br />1 <br /> <br />1 <br />The UTEXAS2 analytical modelling program, analysis method and <br />program options were described in previous sections of this report. <br />As noted above three critical sections were considered in the <br />present analysis. In each case several automatic search trials <br />were performed, varying the initial search input data, to assure <br />that the minimum factor of safety was found. The data for <br />subsurface and modelling conditions have been described in previous <br />paragraphs. Plate 9 of the Appendix presents the profile, <br />parameters used and the resulting safety factor for section A-A. <br />Plate 10 of the Appendix presents the profile, parameters used and <br />the resulting safety factor for section B-B. The profile, <br />parameters used and resulting safety factor for Section C-C is <br />presented as Plate 11 of the Appendix. The Plate 11, Section C-C <br />analysis also includes an evaluation of the pile's backslope or <br />upslope stability. Previous discussions have emphasized 'the <br />suspicion that the pore pressures in the pile and its foundation <br />cannot be reasonably represented by a single phreatic surface. <br />However, data from the current wells do not provide sufficient <br />information to comfortably derive a stability model which either <br />includes multiple phreatic surfaces or pore pressure values. <br />Therefore, it was assumed that the closest approximation of actual <br />pore pressures that can be made based on existing information would <br />be to use the maximum water level measurements to create a single <br />phreatic surface for use in stability calculations. However, as <br />previously discussed, there is a possibility that higher pore <br />pressures exist than are indicated by the open well type <br />16 <br /> <br />