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iii iiiiiiii~iiiiiii <br />999 <br />Rimrock Mine Sediment Pond Slope Stability Analysis_ <br />The sediment pond was constructed in part in 1992 and was <br />modified in the first half of 1993 to lessen the sideslopes to <br />2.5H:1.OV. The survey and site inspections were conducted on <br />December 7 and 22, 1992. A final inspection was conducted on <br />April 22, 1993. <br />Compaction tests were conducted on both sides and the top of the <br />embankment by GSI Geotechnical Services, Inc. in March of 1993. A <br />backhoe was used to dig flat spots along the embankment sides and <br />deeper spots along the top of dam. A Troxler nuclear gage was <br />then used to perform the compaction tests. The results of these <br />compaction tests are enclosed. The weight of the large hydraulic <br />excavator and the Cat D8N on the dam during construction was able <br />to achieve proper compaction, in the order of S5A; to 90~ of the <br />maximum dry density. This was also verified in the final <br />inspection. During the additional work to lessen the embankment <br />slopes to 2.SH:1.OV, a keyway was established between the old <br />embankment and the newly added fill to prevent sliding along the <br />plane between the two surfaces. The keyway and all fills were <br />compacted to 85~ to 90SK of the maximum dry density. <br />The last site inspection revealed no evidence of cracking, <br />bulging, sliding, seepage or other construction problems. Samples <br />of the pond embankment material were obtained in early June of <br />1993 and submitted to GSI Geotechnical for triaxial shear <br />testing. <br />The results of the testing are shown in the enclosed in the <br />letter from GSI Geotechnical to Mark Kerr dated July 29, 1993. <br />This results of the compaction testing, the shear testing and the <br />site embankment measurements are used to determine the slope <br />stability of the embankment. <br />The average current slope of the pond embankment is approximately <br />2.5H:1.OV, although it does vary from 2.4H:1.OV to 2.65H:1.OV. <br />The slope length is approximately 40 feet at its greatest point <br />toward the deepest point of the pond, where approximately 5 feet <br />of pond depth has been incised into original ground. Exhibit 1 of <br />this report shows the actual configuration of the pond in detail. <br />The cross-section shown in Exhibit 1 is representative of the <br />embankment at its greatest height, which occurs near the <br />principal spillway pipe. <br />