REP10403 - Laserfiche WebLink

Home Browse Search

merely skimmed the surface of the existing slope, which is believed 1 to be the weathered remnant of an old slide scarp. This would help explain the tenacity of this exceptionally steep slope over time. Test borings at the toe of the slope area appear to indicate that the material is present in an extremely high density. Therefore, we would expect the material to have extremely high shear strength char- acteristics. The wide range of shear strength characteristics avail- able for this material were listed in the earlier section. The effective stress values would be most appropriate where the materials would be anticipated to be subject to saturation and the development of a true, phreatic surface. Considering the steep topography and the highly impermeable nature of the clayey soils in the cut and the 7 foundation area, we feel it would be highly unlikely that saturation 1 and a phreatic condition would develop within these materials. Since the total stress friction angle of 72 degrees obtained for this material is an extremely high and unusual value, we decided to perform a sensitivity analysis in order to sort out the relative effects of shear strength values assumed for this material on the over- all stability analysis. Therefore, stability analyses were performed for three different levels of shear strength in the cut slope and foundation materials. The lowest value utilized was the Peak effective stress friction angle of 34 degrees. On the other extreme, the total 1 stress friction angle of 72 degrees was also utilized. L9e then per- formed the analyses again utilizing an intermediate shear strength value of 50 degrees. The effect of the assumptions on the analyses may be seen on the Table of Stability Analysis Results in the Appendix of the report. With many of the conditions analyzed, the critical I failure circles passed entirely through the existing and new fill -6-