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Mr. Jeff Gregg January 5, 2006 Page 4 MATERIAL PROPERTIES ~~ CIVIL RES'7JU RCES, LLC Overburden The index properties for the insitu clay overburden were based on field testing data and on our engineering judgment; the following parameters have been used to model the overburden. Dry Unit Moist Unit Saturated Unit Cohesion C' psf Friction Angle ~' ° Wei ht cf Wei ht cf Wei ht cf 103 114 126 200 28 Alluvial Sand and Gravel The sand and gravel is generally medium grained sand, medium dense, poorly to well graded, and generally clean. The deposit ranges from fine to coarse sand with some silt and occasional rounded to well rounded gravels less than 2- inches indiameter. The alluvial sand and gravel has been modeled as follows: Dry Unit Wei ht cf Moist Unit Wei ht cf Saturated Unit Wei ht c Cohesion C' psf Friction Angle ~'O 119 129 130 0 35 Claystone Bedrock The proposed mine area is generally underlain by claystone bedrock. Claystone is generally a weak bedrock and is often prone to slope instability and the bedrock foundation strength is critical for the highwall stability. For the claystone bedrock, two potential strength conditions were considered. These strength conditions are referred to as: 1) peak strength, and 2) residual strength. Peak strength is the maximum shear strength the claystone bedrock exhibits. The shear strength is made up of both cohesion (diagenetic bonding) and internal friction. Under short-term conditions for unsheared claystone, peak strength governs behavior. If a sheared sudace or sheared zone is present within claystone as a result of faulting, slippage between beds due to folding, past shrink-swell behavior, stress relief, or from a landslide, the cohesion along the sheared surface is reduced to zero, and the angle of internal friction is decreased, due to alignment of clay minerals parallel to the shear plane. Under these conditions a claystone exhibits its lowest strength known as residual strength. Residual strength bedrock occurs indiscrete zones, parallel with the sheared surface or zone, whereas fully softened strength occurs over a broader area. Based on data from other recent jobs, and engineering judgment, we modeled the claystone as follows: Dry Unit Weight (pcf) Moist Unit Weight (pct) Saturated Unit Weight (pcf) Cohesion C' psf Friction Angle ~' ° 116 124 134 Peak =100 Peak = 28 Residual = 0 Residual = 15 Soil-Bentonite Slurry The proposed slurry wall will consist of a mix of the overburden clay and imported bentonite. The resulting mix will produce anon-Newtonian fluid with some shear strength characteristics based on a reduced friction angle of the overlying clay overburden. Based on engineering judgment, we modeled the slurry wall as follows: Dry Unit Weight (pct) Moist Unit Weight (pcf) Saturated Unit Weight (pcf) Cohesion C' psf Friction Angle 4ti' ° NA 110 122 0 26