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tk <br /> liner system must meet a minimum residual shear strength defined by a friction angle of 10.5 <br /> degrees to achieve the minimum factors of safety against slope instability. In addition to the <br /> interfaces noted in the above-referenced report, the interface between the geotextile cushion <br /> layer and the 60-mil textured HDPE geomembrane must also meet this shear strength <br /> requirement. Based on our experience, the required shear strength can be achieved with proper <br /> selection and testing of the geotextile cushion and textured HDPE geomembrane materials. The <br /> interface shear strength shall be demonstrated using actual geotextile and geomembrane to be <br /> used in Module 1 liner construction in the Contractor's product submittals, and shall be verified <br /> by conformance testing required in the QAM. <br /> 4.0-Recommendations <br /> To protect the 60-mil HDPE geomembrane from the proposed crushed rock, a 16-ozlyd2 <br /> geotextile (non-woven,needle-punched) cushion shall be provided between the crushed rock and <br /> the geomembrane. <br /> The geotextile-textured HDPE geomembrane interface shall meet a minimum residual shear <br /> strength (measured at 3-inch displacement) defined by a friction angle of 10.5 degrees. In <br /> addition to the shear strength requirements previously specified in the construction <br /> specifications, the shear strength of-the geotextile cushion-textured HDPE geomembrane <br /> interface will be demonstrated and verified using direct shear testing (ASTM D5321) before <br /> installation of the liner system. The testing will be performed under: <br /> • Normal Stresses: 3,000,6,000,and 12,000 psf <br /> ® Strain Rate: 0.2-inch/minute <br /> • Minimum Displacement: 3-inches <br /> • Saturation: Test under saturated conditions <br /> N:\sacDP\2003\Prj\83\835608.3ap.doe <br /> (FSL) <br /> 4 <br />