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2.1.1 Geometry <br />A cross-section through the East Slide was developed for the design of seepage control features. This <br />cross-section, shown on Figure 5, includes all known bedrock layers and overlying colluvium. The <br />contact between the bedrock and the colluvium was estimated in most locations, based on available <br />data from surveys conducted as the slide was excavated. A granular drainage blanket and a granular <br />interceptor trench were installed at locations shown in Figures 4 and 5. A layer of carbonaceous shale <br />was identified at the top of the bedrock bench that was exposed during construction. This layer was <br />deemed to be important for stability evaluation as a potential failure surface could penetrate this <br />material. Therefore, a drainage blanket was installed over the bench to improve drainage in this <br />location. <br />2.1.2 Groundwater <br />Groundwater was considered when design recommendations were made for the repair. One 7.5 gpm <br />seep every 50 feet along the length of the slide area was assumed to calibrate a pre -slide seepage <br />model. This resulted in a total head boundary condition on the upslope side of the model of 6,350 <br />feet. Potential seepage face review nodes were placed along the entire ground surface of the model. <br />2.1.3 Modeling Parameters <br />Laboratory testing data along with engineering judgment were used to develop representative <br />geotechnical modeling parameters for the analysis of the slope. <br />Table 1 summarizes the permeability parameters used in modeling. <br />Table 1 Parameters Used in Seepage Analysis <br />Table 2 summarizes the unit weight and shear strength parameters for slope stability modeling. <br />P:\Mpls\06 CO\26\06261003 Haul Road Slide Repair\WorkFtles\Report\MCC_Slump_Repair-Instrumentation-Drain Rev 2012-12-12.docx 4 <br />Colluvium <br />3.28E-09 <br />1.00E-07 <br />Drainage Blanket <br />8.53E-04 <br />2.60E-02 <br />Carbonaceous Shale <br />3.28E-08 <br />1.00E-06 <br />Shale <br />3.28E-08 <br />1.00E-06 <br />Coal <br />3.28E-05 <br />1.00E-03 <br />Sandstone <br />3.28E-06 <br />1.00E-04 <br />Table 2 summarizes the unit weight and shear strength parameters for slope stability modeling. <br />P:\Mpls\06 CO\26\06261003 Haul Road Slide Repair\WorkFtles\Report\MCC_Slump_Repair-Instrumentation-Drain Rev 2012-12-12.docx 4 <br />