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<br />March 22, 1996 <br /> <br />-2- <br />943-2847.001 <br />Using the criteria identified above, two layers of Tensar UX1700 HS geogrid were selected. <br />Design calculations are presented in Attachment A. Typical details are presented in Drawing No. 3 <br />(Revision 1), which is attached. The specifications associated with the manufacturing and <br />installation of the geogrid are provided in Attachment B. <br />The UX1700 HS geogrid will need to be installed as follows: <br />- Excavate a minimum of 12 inches of Soil Liner Fill subgrade. An additional <br />eighteen inches of excavation will be required in areas where the Leak Detection <br />Trench intersects the geogrid reinforced areas. <br />- Place the first layer of UX1700 HS geogrid. Plastic ties may be used to connect <br />the geogrid along the edge of each roll. At the end of each roll, a bodkin <br />connection using a flat HDPE bar should be used to ensure 100% load transfer. <br />Connections should be staggered by approximately five feet. <br />- Place a minimum of 6 inches of Select Structural Fill over the geogrid. <br />- Place the second layer of UX1700 HS geogrid so that the direction of maximum <br />strength is transverse to the direction of maximum strength for the first layer. <br />Plastic ties may be used to connect the geogrid along the edge of each roll. At the <br />end of each roll, a bodkin connection using a flat HDPE bar should be used, to <br />ensure 100% load transfer. Connections should be staggered by approximately five <br />feet. <br />- Place a minimum of 6 inches of Select Structural Fill over the geogrid so [ha[ the <br />fill surface is to finished grade in areas without leak detection trenches and 18 <br />inches below grade in areas with leak detection trenches. <br />- Place a minimum of 18 inches of compacted Structural Fill over the Select <br />Structural Fill in areas with a leak detection trench. <br />During the construction activities, only the Raven Beacon shaft was encountered at the ground <br />surface. No surface expression of the other suspected workings was noted. While a vibratory <br />compactor and construction equipment [raveled over the surface of the slope, no depressions were <br />visible on the surface that could have indicated the presence of subsurface voids. As five of the <br />shafts were not identified, CC&V reviewed site investigations and reports from the previous <br />correspondence in the area of Pad No. 2 to determine if the location of any other underground <br />workings had been previously documented. On June l2, 1990 Aguirre Engineers Inc. (AEI) <br />presented a report to CC&V titled "Geo[echnical Design Studies Report Pad No. 2 Expansion Near <br />Victor, Teller County, Colorado." In this report, AEI identified three underground workings (1,2 <br />and 3) within the proposed limits of the Pad No. 2 Expansion. AEI recommended [hat these shafts <br />be excavated to a depth of l2 feet, and backfilled with a compacted structural fill material. A daily <br />repott prepared by Mr. Button Holt with AEI on August 15, 1990 documents the excavation and <br />backfilling of these workings. <br />On reviewing the base topography used by AEI, prepared by Russell Engineering N 1985, working <br />1 corresponds to Little Nell #3, and working 2 relates to the Ore House shaft. Working 3 does not <br />1CI~REA/U.LTR Golder Associates <br />