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Mr. Mark Johnson <br /> January 2 , 2014 <br /> Page 4 <br /> MATERIAL PROPERTIES <br /> Overburden <br /> The index properties for the insitu clay overburden were based on field testing data and on our engineering <br /> judgment; the following parameters have been used to model the overburden. <br /> Dry Unit Moist Unit Saturated Unit Cohesion C' Friction Angle�'° <br /> Weight c Weight c Weight c sf <br /> 103 114 126 50 29 <br /> Alluvial Sand and Gravel <br /> The sand and gravel is generally medium-grained sand, medium dense, poorly to well graded, and generally clean. <br /> The deposit ranges from fine to coarse sand with some silt and occasional rounded to well rounded gravels less <br /> than two inches in diameter. The alluvial sand and gravel has been modeled as follows: <br /> Dry Unit Moist Unit I Saturated Unit Cohesion C'psf Friction Angle 0'* <br /> Weight(pco Weight(pco I Weight c <br /> 119 129 130 0 35 <br /> Claystone Bedrock <br /> The proposed mine area is generally underlain by claystone bedrock. Claystone is generally a weak bedrock and is <br /> often prone to slope instability and the bedrock foundation strength is critical for the highwall stability. For the <br /> claystone bedrock,two potential strength conditions were considered. These strength conditions are referred to as: <br /> 1) peak strength, and 2) residual strength. <br /> Peak strength is the maximum shear strength the claystone bedrock exhibits. The shear strength is made up of <br /> both cohesion(diagenetic bonding)and internal friction. Under short-term conditions for unsheared claystone, peak <br /> strength governs behavior. If a sheared surface or sheared zone is present within claystone as a result of faulting, <br /> slippage between beds due to folding, past shrink-swell behavior,stress relief, or from a landslide, the cohesion <br /> along the sheared surface is reduced to zero, and the angle of internal friction is decreased, due to alignment of <br /> clay minerals parallel to the shear plane. Under these conditions a claystone exhibits its lowest strength known as <br /> residual strength. Residual strength bedrock occurs in discrete zones, parallel with the sheared surface or zone, <br /> whereas fully softened strength occurs over a broader area (not used in this modeling). Based on data from other <br /> recent jobs and engineering judgment,the residual strength claystone was modeled in a five-foot thick layer <br /> overlying the peak strength bedrock as follows: <br /> Dry Unit Moist Unit Saturated <br /> Weight(pco Weight(pco Unit Weight Cohesion C'psf Friction Angle V° <br /> 116 Peak= 126 Residual -_Peak= 135 Peak= 100 Peak=25 <br /> Residual = 110 133 Residual =0 Residual = 15 <br />