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4.3 Friction Angle Estimation <br />In early LF&4 annual quarry evaluation reports (L&A, 1997-2002), a total <br />representative angle of friction (~ + i) = 40° was used for the wedge stability <br />analysis, where "~" was the basic friction angle and "i" was the surface <br />roughness angle (Hoek and Bray, 1977). The surface roughness angle is the <br />angle between the basic plane of the joint and the planes representing the <br />surface of ripples or undulations of the joint surface. This value was based on <br />our research of the subject, including published data from various sources, and <br />' was a reasonable estimate given that no actual laboratory testing had been <br />performed previously on rock from the quarry. However, as a result of the 2003 <br />' geotechnical investigation, 20 rock samples were selected for direct shear <br />testing in order to better define the strength of the rock (L8u4, 2003). The test <br />' results produced only a basic friction angle, ~, and indicated that the basic <br />friction angle of the discontinuities ranged from 13.7° to 49.3° with a mean value <br />of 28°. These results do not include the two direct shear tests run on samples <br />with clay material along the foliation plane, which produced an average friction <br />' angle of only 5°. <br />For this current study, a basic friction angle of 28° plus a surface roughness <br />angle of 5° (total of 33°) has been used for all of the wedge stability analyses. <br />This approach of using ~ + i to represent the friction angle of the rock differs from <br />the Mohr-Coulomb strength criterion utilized in the 2003 geotechnical <br />investigation and slope stability analysis. It was chosen to use ~+i for this <br />investigation due to the geometric input constraints of the stereonet and the <br />wedge stability analysis used in this study. The Mohr-Coulomb approach <br />includes both a friction angle and a cohesion value to define the shear strength <br />of the discontinuities, where the cohesion value is used to account for "the <br />interlocking of asperities on the matching surfaces of the joint, and the increase <br />in shear strength given by this interlocking..." (Hoek, 2000). <br />9- <br />