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PN: 50663GE <br />November 20, 2006 <br />The material properties used in the analysis are shown below. <br />Material Pro a Soil 1 Soi] 2 <br />Soil Type Clay Claystone Formation <br />Soil Model Mohr-Coulomb Mohr-Coulomb <br />Unit Weight 125 pcf 145 pcf <br />Cohesion 180 1000 <br />Phi 27 30 <br />Due to the possible variation in material properties, a sensitivity analysis was performed which <br />models the stability of the slopes with variations in material properties. The results of the <br />sensitivity analyses aze shown in Appendix A. The results indicate that even with a wide range of <br />material properties, the factors of safety will still be above 1.5 without the use of retaining <br />structures except at section 5+00 on the cut side and section 12+00 on the embankment fill side, <br />where the factors of safety aze 1.47. These areas may need additional retaining structures to <br />obtain the desired theoretical factor of safety of 1,5 <br />If a stable geometry cannot be established using conventional design and construction <br />techniques it may be necessary to consider walls that aze designed with additional resistance to <br />movement through the use of tieback anchors such as rock bolts or soil nails. There may be <br />additional techniques and methods for soil retention, such as mechanically stabilized earth <br />structures that may be viable options for this site. We aze available to discuss these concepts <br />with you. <br />As we discussed above we encountered subsurface water within the soil mantle at about two (2) <br />feet above the Animas Formation in Test Borings One, Two and Three. The theoretical factor of <br />safety was reduced to 1.47 in Section 5+00 and 12+00 when pore pressure was included in the <br />slope stability analysis. Pore pressure reduces the strength of the influenced soil and therefore <br />can significantly reduce the integrity of the sloped soil. We should be contacted during the initial <br />stages of the roadway construction to evaluate any areas where subsurface water is encountered. <br />The strategy will be to develop subsurface drain systems at strategic locations, if necessary to <br />reduce the potential for development of pore pressures within the soils adjacent to the roadway. <br />6.0 RETAINING STRUCTURES <br />We understand that laterally loaded walls or structures may be constructed as part of this site <br />development. Lateral loads will be imposed on the retaining structures by the adjacent soils and, <br />14 TRAUTNER ~ <br />A DIViS10N OF TRIGONHidil <br />