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Mr. David A. Kidd, P.E. <br />29 September 1993 <br />Page 3 <br />GEOSYNTEC CONSULTANTS <br />device containing an upper and lower shear box. The upper box measures <br />12 in. by 12 in. (300 mm and 300 mm) in plan and 3 in. (75 mm) in depth. <br />The lower box measures 12 in. by 14 in. (300 mm by 360 mm) in plat and <br />3 in. (75 mm) in depth. The test conducted at a normal stress; cf 300 psi <br />(2,100 kPa) used a smaller upper and lower shear box. The smaller upper <br />box measures 6 in. by 6 in. (150 mm and 150 mm) in plan and 3 in. (75 mm) <br />in depth. The smaller lower box measures 6 in. by 8 in. (150 mm by 200 <br />mm) in plan and 3 in. (75 mm) in depth. <br />A summary of the test equipment and conditions used to conduct the <br />interface direct shear tests is presented ir. Table 2. This table <br />indicates the size of the shear box, the initial compaction condition for <br />the soils (i.e., dry unit Wight and moisture content), consolidation <br />stress, time for consolidation, the moisture content of the soils at the <br />completion of testing, the normal stress applied to the soil in the upper <br />shear box during testing, and the horizontal displacement rate for each <br />test. <br />The interface direct shear test series was conducted specifcally to <br />evaluate the strength of the weakest (i.e., the lowest shearing <br />resistance) interface between the three lining system components. The <br />geomembrane was placed between the crushec rock overliner material and <br />the iron clad tailings and not secured to either of the shear boxes. <br />With this method of specimen preparation, shear failure would likely <br />occur at the weakest interface within the test cross section. <br />For each test in the test series, the tailings were moisture - <br />conditioned and compacted into the lower shear box by hand tamping to the <br />reported dry unit weight for each normal stress condition as specified <br />by Golder. The target dry unit weight and noistLre content corresponded <br />to 95 percent of the maximum dry unit weight and the optimum moisture <br />content, based on the results of standard Proctor compaction tests <br />provided by Golder. In each test, the overliner material under its <br />as- received moisture conditions was compacted directly on the top of the <br />GL3458/GEL93234 <br />