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5 . Long-Term Stability of Backfilled Slope <br /> During the Fall of 1993, samples of fill material were gathered <br /> from the roads and the mine portal areas . At each sample area , <br /> approximately 100 to 200 lbs . of material was gathered over roughly <br /> 1 /2 acre, gathering some material from the surface and some from <br /> digging with a shovel . In all cases , the material gathered was <br /> representative of the material which would be used in backfilling . <br /> A 1 1 samples were sent to CTL Thompson in Denver for sieve analysis , <br /> plasticity indexes , liquid limits , optimum moisture content , <br /> maximum dry density and direct shear tests to determine the <br /> cohesion and internal angle of friction of the material . All lab <br /> test data is included in Appendix A. <br /> As can be seen from the analyses , the percent silt and clay of the <br /> materials (passing No . 200 sieve) range from 1 1% to 32% - This <br /> demonstrates the lack of fines in much of the material . Also, the <br /> low plasticity indexes , ranging from 9 to 11 , confirm the lack of <br /> appreciable clay in the material . For this reason , it is not likely <br /> that the material will expand or contract to a large extent after <br /> backfilling ; therefore , consolidated swe11 tests have not been <br /> performed . Slake durability tests were performed on the samples and <br /> the results show that the material is not readily weathered and <br /> does not exhibit much shrink swell potential . However , water <br /> infiltration is very likely due to the coarse nature of the <br /> material and this is accounted for in the slope stability analyses <br /> through use of a pore pressure ratio . Overall , the test results <br /> show that the materials from portal excavation have slightly better <br /> strength properties than that of the roads . The tests show a <br /> surprisingly high cohesion for the material from Mine #4 . <br /> The hard, durable and angular nature of the material with little <br /> clay indicates that it should possess little cohesion but should <br /> have relatively high internal angles of friction . The results of <br /> the direct shear tests show this to be the case . These tests were <br /> performed under the consolidated-undrained condition and the <br /> samples were compacted to 90% of their maximum dry density prior to <br /> testing . Only that material that passed the #4 sieve was tested in <br /> the direct shear apparatus . Larger particles cannot be used . <br /> Therefore , it must be considered that , for each test , a large <br /> portion of the material is not being tested . This larger size <br /> material will have large friction angles and very low cohesion . <br /> Since some moisture is present in the samples during shear testing , <br /> the resulting failure envelope , when plotted, can show an "apparent <br />