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Friction Angle Estimation <br />In early LF&A annual quarry evaluation reports (L&A, 1997-2002), a total <br />representative angle of friction (~ + ~) = 40° was used for the wedge stability <br />analysis, where "~" was the basic friction angle and "P' was the surface roughness <br />angle (Hoek and Bray, 1977). The roughness angle is the angle between the <br />basic plane of the joint and the planes representing the surface of ripples or <br />undulations of the joint surface. This value was based on our research of the <br />subject, including published data from various sources, and was a "best guess" <br />given that no actual laboratory testing had been performed previously on rock <br />from the quarry. However, as a result of the 2003 geotechnical investigation, 20 <br />rock samples were selected for direct shear testing in order to better define the <br />strength of the rock (L&A, 2003). The test results produced only a basic friction <br />angle, ~, and indicated that the basic friction angle of the discontinuities ranged <br />from 13.7° to 49.3° with a mean value of 28°. These results do not include the <br />two direct shear tests run on samples with clay material along the foliation plane, <br />which produced an average friction angle of only 5°. <br />For this current study, a basic friction angle of 28° plus a roughness angle of 5° <br />(total of 33°) has been used for all of the wedge stability analyses. This <br />approach of using ~ + i to represent the friction angle of the rock differs from the <br />Mohr-Coulomb strength criterion utilized in the 2003 geotechnical investigation <br />and slope stability analysis, but is utilized due to the geometric input constraints <br />of the stereonet and the wedge stability analysis used in this study. The Mohr- <br />Coulomb approach includes both a friction angle and a cohesion value to define <br />the shear strength of the discontinuities, where the cohesion value is used to <br />account for "the interlocking of asperities on the matching surfaces of the joint, <br />and the increase in shear strength given by this interlocking..." (Hoek, 2000). <br />-9- <br />