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4.0 Analyses of Corrective Measures <br />In accordance with the observational approach, the overall stability of the landslide was analyzed <br />and then detailed analysis of selected corrective measures were made. The overall landslide <br />stability was analyzed using groundwater models with hand calculations and limit equilibrium <br />computer methods with hand calculations for slope stability. Detailed analyses of the pins and <br />RCC buttress were made using explicit Emile difference methods of analysis and hand calculations. <br />The analyses of corrective measures were based upon aback-calculation of pre-correction <br />conditions and the increase in stability with the corrective measures. Three primary factors for <br />determining pre-correction stability are the location of the shear plane, the strength of the <br />shearing zone, and the pore pressures within the landslide. The shear plane was established using <br />inclinometers, the in-situ shear strength along the shear plane was determined using the borehole <br />shear test (BHST), and the pore pressures were measured from piezometers. Table 1 summarizes <br />the geotechnical parameters used in the analyses. Figure 2 shows the piezometric levels used in <br />the analysis. This information was used to model the groundwater and the slope stability of the <br />• landslide. <br />4.1 Groundwater Analyses <br />Since groundwater is the primary trigger to landslide movement, an approximate groundwater <br />model using finite element methods (SEEP/W) was developed to match known stratigraphy and <br />existing piezometric levels. The primary purposes far the groundwater model are to provide: <br />(1) an approximation of the overall groundwater regime, (2) an approximation of the <br />hydrogeological interconnections between stratigraphic units if the groundwater regime is altered, <br />and (3) pore pressures within the landslide for stability analyses. The model seems to verify that <br />the groundwater is from near surface sources at the head of the landslide and that the ponds <br />contributed to the high water levels at the toe. The groundwater models used for the initial and <br />dewatered conditions is in Appendix C. <br />4.2 Limit Equilibrium Slope Stability Analyses <br />A limit equilibrium analyses was used to predict the factors of safety with the pins installed and <br />with dewatering at the head, body, and toe of the slope. Spencer's Procedure of Slices using the <br />• computer program SLOPE/W was used because it satisfies all conditions of equilibrium and allows <br />0626024\58991-UABM 7 <br />