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_'00Y > <br />I t,.1 1 0 <br />Shear Strain <br />(inches per inch) <br />0.00 to 0.02 <br />0.02 to 0.04 <br />0 04 to 0.06 <br />0 06 to 0.08 <br />1 figure 19. Sectional Viemv of Failure Surface, Shear Strain Case 3, Factor of Safety 1.51 <br />' A tOurth model was run using what is believed to be the least stable till properties. <br />unit eathercd shale material with fair compaction. 'This model resulted in a factor of safety of <br />' 1.45: while this is below the desired lone-term factor of safety of 1.50, it is verv unlikely that this <br />Condition Could exist. The nature of the K-Pit stratigraphy makes it very unlikely that the entire <br />fill would be comprised of shale material, as the upper stratigraphic layers are largely sandstone. <br />' I'his sandstone material will be the first to be stripped and placed in the Ilorse Gulch till. To <br />Sr?nulate the possible layering of the I lorse Gulch till a fifth model was ntn using the properties <br />t6r a mix of rock and soil that is predominantly rock. This resulted in a factor of' safety over <br />' 1.75. r <br />3.1 Discussion <br />' These modCIN show with little unCertainty that the clay subgradc is the weakest link in the <br />I lurk Gulch fill. I lowever, it is stable xvith a factor of safety greater than 1.5 for the cases that <br />' \\ ill most likely be encountered. Comparing the shear stain models gives the best representation <br />of the potential failure surfaces. Shear strain results for all three cases modeled are presented as <br />I i<?ure 20. <br />3.2 Summary <br />Specific conclusions that can be drawn from these analyses are summarized by the <br />following points: <br />• The weak clay seam is most likely the slip plane, primarily because it is the weakest layer <br />in the geologic seduence. <br />The model indicates that the clay layer tails. The mass of material above the clay fails <br />due to tensile failure of the upper layers. This failure mechanism results in movement of <br />the dump face down I lorse Gulch. <br />Agapito .Associates. Inc.