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The primary geotechnical parameters for predicting slope stability include shear strength, <br />angle of repose, weathering of rock, moisture content and stability of the underlying <br />foundation. <br />Shear Strength <br />Exhibit 6.5 <br />Geotechnical Stability <br />CM -25 Mine Permit Amendment <br />M- 1977 -307 <br />Shear strength is calculated using the Mohr- Coulomb failure criterion (Fredlund et al., <br />1996). The shear strength of granular soil is frequently characterized by the angle of <br />internal friction ( y5 ) and cohesion (C), as follows: <br />= c ' +(an— uw) tan (p' [1] where: <br />i = shear strength <br />c' = cohesion intercept (due to adhesion, cementation, stress history, <br />interlocking of particles, etc.) <br />(p' = effective angle of internal friction <br />an = total normal stress on the plane of failure <br />(an— uw) = effective normal stress on the plane of failure <br />uw = pore -water pressure. <br />While shear strength (i) was not calculated specifically for the waste rock pile at CM -25, <br />there is sufficient data from similar waste rock piles to infer that the shear strength of the <br />pile at CM -25 will yield values sufficient for a stable slope. <br />The angle of internal friction angle is a function of the following parameters (Hawley, <br />2001; Holtz and Kovacs, 2003): <br />1. Particle shape and roughness of grain surface (friction angle typically increases with <br />increasing angularity and surface roughness): <br />CM -25: The waste rock is blasted and thus consists primarily of rough edged <br />materials. <br />2. Grain quality (weak rock materials such as shale have lower friction angles compared <br />to strong rock materials such as granite) <br />CM - 25: Waste rock is primarily sandstone, a semi weak rock <br />3. Grain size (friction angle increases or decreases with increase in grain size) <br />CM -25: Waste rock has been blasted so it ranges in size from small boulders to <br />medium pebbles. <br />GS -1 <br />