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S i <br />SMITH WILLIAMS CONSULTANTS, INC. <br /> <br />configuration was allowed to consolidate overnight before the shear strength test was . <br />performed. This yielded a friction angle of 17 degrees and a cohesion of 1,315 psf. <br />Draft test results were presented to the DBMS by CC&V in a January 9, 1996 letter <br />titled "Cresson Project.• Permit M-80-244: Procedures and Materials for 1996 <br />Construction." A copy of the interface shear strength results is presented in <br />Appendix B. In February 1998, the interface testing was repeated for four different <br />normal stress values ranging between 50 and 300 psi imposed on a section of clay <br />borrow SLF .overlain by 100-mil textured LLDPE geomembrane overlain in turn by <br />LVSCF. This yielded a residual friction angle of 18 degrees and a cohesion of 865 <br />psf. Therefore, in order to represent the clay borrow SLF / 80-mil textured LLDPE <br />geomembrane /DCF configuration; an angle of internal friction of 18 degrees and no <br />cohesion were used in the analysis. These test results are presented in Appendix B. <br />As part of Amendment No. 8, additional interface testing was conducted at 500 psi. <br />The test results indicated an interface shear strength with a friction angle of <br />17 degrees and zero cohesion is appropriate for this soil liner configuration. A copy <br />of these test results are presented in Appendix B. <br />• 4. Phase 5: Interface shear strength testing performed as part of the design for the <br />Phase 5 VLF ore storage area consisted of SLF overlain by 80-mil textured LLDPE <br />liner (textured side down) overlain by DCF. Interface shear strength testing was <br />performed for normal loads of 50, 100, 150, and 200 psi. The interface testing for <br />these normal loads was used to define a linear relationship (friction angle and <br />cohesion) between the normal loads calculated in the stability section slices and the <br />corresponding shear strength. The SLF was compacted to 95 percent of the standard <br />Proctor maximum dry density and at 2 percent above the.optimum moisture content: <br />- At large strain (45 mm), the residual interface shear strength had a friction angle of <br />23.5 degrees. At low stress, the failure surface developed between the geomembrane <br />and the DCF. At higher stresses, the failure surface developed between the <br />geomembrane and the SLF. For the stability analyses, an interface friction angle of <br />18 degrees was used-to introduce conservatism into the-design. No further interface- <br />testing was conducted for the PSSA composite liner systems because these materials <br />were already tested as part of the Phase.IV VLF design. <br />Foundation Material, For the stability analyses, the foundation material shear strength was <br />modeled with an angle of internal friction of 40 degrees and no cohesion, which represents either <br />a bedrock foundation or a granular fill foundation. The results of the geotechnical investigation <br />S:\PROJECTS\1125 CCBV PHASE 5 VLF1H2 - DESIGMAREQUA VLF\VLF PHASE 5 FINAL REPORT V2.DOC 33 <br />