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® 5.2.2 Interface/Internal Shear Strength Data Interpretation <br />The interface/internal shear strengths specified above are defined in terms of a friction <br />angle alone (which was done to simplify the slope stability analyses). It is likely that the <br />interface/internal shear strength envelopes measured from direct shear tests would be <br />non-linear and show both adhesion and friction. Therefore, the following procedure is <br />recommended while evaluating the measured shear strength test data: <br />• If the measured residual Mohr -Coulomb failure envelope (within a normal <br />stress range of 0 to 12000 psf) plots entirely above the failure envelope defined <br />by a friction angle of 10.5 degrees, the shear strength is acceptable. <br />• If the measured residual Mohr -Coulomb failure envelope (within a normal <br />stress range of 0 to 12000 psf) plots entirely below the failure envelope defined <br />by a friction angle of 10.5 degrees, the shear strength is not acceptable. <br />• If a major portion of the measured residual Mohr -Coulomb failure envelope <br />(within a normal stress range of 0 to 12000 psf) plots above that defined by a <br />friction angle of 10.5 degrees (and only a small portion of the measured <br />envelope plots below), additional slope stability analysis should be performed <br />to determine whether the measured shear strength results in acceptable factors <br />of safety. <br />\\SACRFPI\COMMON\sacDP\2002\1>RAPJ8\83\835608.2bz.doc EMCOWOW]', Inc. <br />Rev_ 0, 07/31/02 <br />5-3 <br />