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Ralston Quarry Slope Stability <br /> LABORATORY TESTING <br /> Samples retrieved from our test holes were examined and visually classified in the <br /> laboratory by the project engineer. Laboratory testing of soil samples included standard <br /> property tests, such as natural moisture contents, dry unit weights, grain size analyses, <br /> and Atterberg limits. Direct shear strength testing was performed on both relatively <br /> undisturbed samples and remolded disturbed (bulk) samples. Laboratory tests were <br /> performed in general accordance with applicable ASTM protocols. Results of the <br /> laboratory index testing are summarized in Table 1. Gradation plots are provided in <br /> Figures 13, 14 and 15. Plots of the direct shear strength data obtained are provided in <br /> Figures 16, 17 and 18. <br /> SUBSURFACE CONDITIONS <br /> Soils and Bedrock The test holes penetrated from about 1 foot to at least 16 feet of <br /> mine tailings placed on the west-facing side of the ridge. Due to encountering refusal at <br /> several locations, the tailings likely are significantly deeper, commonly. Up to about 25 <br /> feet of tailings were present along much of the central portion of the slope prior to the <br /> 2017 slope failure. Similar soils, relocated to the stockpile, were encountered in Test <br /> Holes 10 and 11. The tailings consist of fragments of shale and igneous rock <br /> (shosohonite) up to cobble- and boulder size, as well as clay and sand. Some of the <br /> tailings remain as placed, other volumes were displaced by prior slumping and some in <br /> the relative recent slope failures. A few inches of poorly developed topsoil had <br /> developed on the tailings at Test Hole 1. <br /> The tailings had been placed on about 6 to 12 feet of native, clayey colluvial soils. At <br /> Test Hole 2, however, some displaced tailings overlay the Pierre Shale materials. <br /> Beneath the surficial fill and native soils, the test holes encountered Pierre Shale <br /> materials to the depths explored. Locally, the Pierre Shale consisted of clean to sandy <br /> clay shales that were hard to very hard. The uppermost several feet of the shales <br /> typically were severely weathered. <br /> More detailed descriptions of these materials are provided on Figures 11 and 12. <br /> Job No. 18-3046 GROUND Engineering Consultants, Inc. Page 5 <br />