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Tri-Cmmty Gravel <br />#576-07 <br />12/19/07 <br />\j Huddleston-Berry <br />riy r"Or MZA Te iAg. I:LC <br />iLaboratory Testing <br />Select soil samples collected in the borings were tested in the HBET geotechnical laboratory for <br />natural moisture content and. density, grain size analysis, and Atterberg limits determination. <br />The laboratory testing results indicate.that the silty sand and'sandy silt soils are non-plastic. The <br />clayey sand soils were shown to be slightly plastic. Laboratory testing results are included in <br />Appendix B.. <br />Dike Construction <br />A generalized profile of the dike based upon the results of the subsurface investigation is <br />included in Appendix C. Based upon_the,results of the borings, HBET speculates that the central <br />and western portions of the dike were constructed immediately above the shale. bedrock. <br />However, Boning B-3 encountered sandy gravel soils above the shale bedrock at depth. As a <br />result;, HBET speculates that the eastern portion of the dike was constructed above unmined <br />gravel in .this.area. <br />In general, it -appears that gravel fill was placed in the dike along the Gunnison River as shown. <br />on the original construction drawing (included in Appendix Q. However; the borings did not <br />encounter significant gravel'in the eastern portion of the dike where it was: shown on` the original <br />drawing. In addition,.based upon thexesults of the borings and laboratory testing, clay soils were <br />not used in the core of the dike.. The contractor involved in the construction of the dike stated to <br />HBET that the overburden materials from other mined areas of the site were used to build the <br />dike. As indicated on the boring logs; this material consists primarily of sandy silt, silty sand, <br />and clayey sand soils. <br />Engineering Properties <br />As indicated on the logs, the in-place dry density of the silt and sand soils used to construct the <br />dike ranged from. 105 to 114 pc f. This corresponds to bulk unit weights of between <br />approximately 120 and 1:30 pcf However, as indicated on the logs of B-1 and B-2, soft, wet <br />soils were encountered -at the base--of the dike above the shale bedrock. In these soils, Standard <br />Penetration Test (SPT) blow counts (1V-values) ranged from 5 to 7 blows-per-foot. These soils <br />may have a much lower density than-the soils above. HBET anticipates that: the bulk unit weight <br />of these materials is around 105 pcf. <br />With regard to conducting stability analyses on the dike, HBET recommends the following <br />engineering parametembe used: <br />Sandy Gravel Soils <br />y = 130 pcf <br />0 = 34° <br />c= 0 psf <br />Sandy Silt,. Silty Sand, and Clayey Sand Soils <br />y = 120 pcf <br />is = 28° <br />c = 0 psf <br />2 <br />ZA2007 Omiects\576-07 Tri County'Dike.Unitcd Companies 1200 - Gco1576-07 LR121867:d6c