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GEOTECHNICAL STABILITY EXHIBIT EXHIBIT U <br />There are no buildings or structures outside the permit area which could be affected by the <br />operation. The 2009 Amendment utilizes a change in the mining slope to maximize the resource <br />within the permit area. The overburden on the west side of the property will continue to be mined <br />at a slope of 2H: IV. This overburden is approximately 20 feet high. However, the gravel of <br />approximately 30 feet height will be extracted to a vertical slope. See Figure U-1. Slope stability <br />issues only apply to the western portion of the operation, since the eastern portion daylights the <br />gravel on a flat surface at the elevation of the mine bench. To the north of the access road, there <br />are no structures outside the permit boundary within a reasonable distance. The Cugnini irrigated <br />field is located west of the permit boundary here. To the south of the access road, a barbed wire <br />property fence is the closest structure (within a few feet of the permit boundary). The following <br />engineering details demonstrate that there will be no slope stability issues with this design and all <br />off site structures will be safe. <br />Design factors <br />1. As a professional engineer with over 30 years in slope stability, I have inspected the interior <br />vertical slopes at the Cugnini Pit for 6 years (2002 through 2008) and found them to be <br />extremely stable in both the gravel and the overburden. The overburden has significant clay that <br />has been very consistent in its ability to resist any type of slope failure. Vertical slopes can <br />remain in place for years without any sign of the slightest failure. There are no slick surfaces and <br />no water that is present in the material at any time during the year that could compromise <br />stability. This is also true of the gravel. The clay content in the gravel is also high, which results <br />in a high reject rate for certain washed products at the mine site. This clay content, combined <br />with precipitate cementing over thousands of years, has resulted in a material that has very strong <br />stability characteristics in both cohesion and internal angle of friction. <br />2. Dozers push the overburden and the gravel downhill to a loader which loads the material for <br />processing at the mine bench level. The dozers require significant force to break up the material <br />for loading, even with a downhill push, further confirming the stability of the material. <br />3. In the extremely remote case that a slope failure would occur, if the slope failed up to the <br />permit boundary, Figure U-1 shows the slope angle that would occur. The horizontal distance <br />from the edge of the excavation to the permit boundary south of the mine access road is 49 feet. <br />To the north of the access road, the distance is 44 feet. South of the access road, the failure angle <br />would be 17.2 degrees or 3.2H:1 V. North of the access road, the failure angle would be 18.2 <br />degrees or 3H:1 V. Both of these angles are far milder than normal failure angles in material that <br />gets strength from internal angle of friction. Figure U-2, from Huang shows typical internal <br />angles of friction for various materials. Assuming that the overburden material is classified as <br />ML-CL, mixture of inorganic silts and clays, this material has an internal angle of friction of <br />approximately 32 degrees. Assuming that the gravel is classified as GC, clayey gravels, poorly <br />graded gravel - sand - clay, this material has an internal angle of friction of approximately 34 <br />degrees. <br />Cugnini Pit, November 2009 U-1