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• for noncircular failure planes. In the limit equilibrium model, the pins are assigned an effective <br />strength based upon the number of'rows, spacing, and strength of the pins. The groundwater <br />model results are directly incorporated interactively into the limit equilibrium model for <br />determining the pore pressures and the effect of dewatering and/or increased infiltration. The <br />slope stability model used for the initial condition in the analyses, the pins and dewatering are <br />presented in Appendix C. The groundwater model for dewatering is also presented in Appendix C. <br />Results of the modeling, as shown on Figure 6 indicate that the factor of safety for initial <br />conditions was 1.06 and would be increased by about 16 percent with the pins installed. The <br />factor of safety would be further increased with dewatering. The dewatering effect, however, is a <br />function of the amount of head decrease and where dewatering occurs on the landslide. The <br />groundwater model was used to evaluate this dewatering effect. <br />The proposed dewatering trenches installed at the head of the landslide will increase the factor of <br />safety to about 1.3 (adjusted factor of safety of 1.26) if the piezometric levels change 30 Feet. <br />Figure 6 is a graph showing the increase in factor of safety with the pins and with different <br />dewatering conditions. <br />• Although Figure 6 indicates that the proposed dewatering trenches at the head are more effective <br />than the stone columns and stone filled pins at the toe, the limit equilibrium analyses does not <br />take into account the increased strength gained over time with the ponds lined and the landslide <br />body dewatered. It also does not take into account the wmbined effect of dewatering the head, <br />body and toe of the landslide at the same time. Therefore, since the stone columns and the gravel <br />filled pins are slowly dewatering the body and toe, the actual factor of safety will be greater than <br />that indicated on Figure 6. <br />4.3 Pin (Micro-Pile Analyses) <br />The design of the pins and their effect on the stability of the landslide was further evaluated using <br />an explicit (mite difference model (FLAG) (Brandshaug, 1998). The analyses also provided the <br />mobilized shear and moments in the pins for structural design. <br />The FLAG analysis used aback-calculation to predict the movement of the landslide and to assign <br />geotechnical parameters in the analysis and then predicted the movement of the landslide at the <br />toe with the pins installed. Table 1 lists the geotechnical parameters used in the FLAG analysis. <br />• Appendix B shows the models of the landslide and the deformation for initial conditions. The <br />oszsoza~ssssi-vASM <br />