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• 2. RCC Buttress <br />The RCC buttress consists of a 10-foot thick roller compacted wncrete (RCC) at the toe of the <br />landslide in the area of the screening plant, as shown on Figures 1 and 4. The RCC buttress is <br />anchored with three rows of 1~~-inch diameter rock bolts spaced about 12 feet apart <br />(approximately 170 total rock bolts). Construction of the RCC buttress addition in 1997 was <br />an emergency response to excessive movement at the toe which endangered the screening <br />plant. A detail of the RCC buttress is presented in Appendix B. <br />3. Dewatering Wells <br />Five dewatering wells were installed around the perimeter of the landslide as part of a Pilot <br />Study to determine if groundwater could be intercepted before it reached the landslide. Well <br />Nos. W-1 and W-2 near the substation and portal, respectively, showed the most potential for <br />dewatering capabilities and, as a result, two additional wells were installed in the vicinity of <br />the substation. These wells were located outside of the scarp area, as shown on Figures 1 and <br />4, so they would not shear during landslide movement. A detail of a dewatering well is shown <br />in Appendix B. <br />• <br />4. Stone Columns <br />Stone columns are gravel-filled bore holes 42 inches in diameter extending from the surface to <br />the underlying cobble layer (alluvium). Figures 1 and 4 show the location of the stone <br />columns. The concept of the stone columns is to drain the pressurized sand layers within the <br />landslide mass by gravity. The upper portion of the stone columns are sealed to prevent <br />surface water from draining into the stone columns and the underlying cobble layer. A detail <br />of a stone column is shown in Appendix B. <br />5. Horizontal Wells <br />Horizontal wells were installed to drain the cobble layer (alluvium) beneath the colluvium in <br />the event excessive amounts of water entered this layer from the stone columns. The <br />horizontal wells drain by gravity. Figures 1 and 4 show the location of the horizontal wells. <br />• <br />os2soza~ssssi-vAB1K 4 <br />