2009-09-21_REPORT - C1981010 - Laserfiche WebLink

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May 29, 2009 Page 9 Table 7. Material Properties and Factors of Safety by Material Type Angle of Slope-W Internal Factor Failure Material Description Friction Cohesion of Surface (degrees) (psf) Safety Rock spoil 37.0 0 2.18 Clay Mix of rock and soil (rocky) 30.0 400 1.91 Clay Mix of rock and soil (average) 20.0 1,300 1.67 Clay Mix of rock and soil (more soil) 10.0 2,000 1.38 Spoil Shaley material fair compaction 20.0 200 1.38 Spoil Weathered shale well compacted 15.0 1,500 1.58 Clay Weathered shale fair compaction 15.0 1,000 1.43 Spoil The construction techniques of the Horse Gulch fill and the K-Pit Buttress will dictate the actual physical properties of each embankment. Dragline placement will have a lower relative compaction than truck placement. Grading the fills to their final contours will break down the material and compact it. Depending on the degree of degradation this process can reduce the angle of internal friction; however, the degree of compaction can increase the angle of internal friction as well as the cohesion. With materials that break down into clays, this interrelationship between the angle of internal friction and the cohesion can present a large range of options. Trying to model each area based on its construction would be difficult at best and would only be accurate for that scenario. AAI's initial approach was not to model for the worst case but rather the worst reasonably expected case. 2.4 Horse Gulch Model Boundary Conditions Model boundaries respond as if there is material beyond the limits of the model. The four vertical sides (i.e., east, west, north, and south sides) are roller boundaries with a zero- displacement condition, which means the geometry outside the model mirrors the geometry inside. This is accurate because mining is generally not near the boundaries and their location has been selected as a line of geometric symmetry. The ground surface was unrestrained and the model base had a zero-displacement condition to simulate rock to an infinite depth. Vertical stresses were determined based on gravitational loading of the material and horizontal stresses assumed lithostatic loading from vertical stresses according to Poisson's effect (vll-v). 2.5 Horse Gulch Groundwater Conditions There are no piezometers located in the footprint of the Horse Gulch fill. All of the available information on the hydrologic conditions in the area is from site visits by Capstone Enterprises West, LLC and AAI personnel throughout the year and the April 2008 drilling program. During the spring thaw, the topsoil is very moist to saturated, free-flowing water was observed in the topsoil. The soft, saturated topsoil is shown in Figure 8. Below the topsoil there was no evidence of free water; samples were only described as moist (Figure 9). Agapito Associates, Inc.