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<br />I <br /> <br />I <br />I- <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />II. <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br />I- <br /> <br />I <br /> <br />. <br /> <br />- <br /> <br />SUMMARY AND CONCLUSIONS <br /> <br />This report presents the results of geological and geotechnical <br /> <br /> <br />investigations performed at Cone Reservoir to be used for feasibility <br /> <br /> <br />considerations involving an enlargement of the existing dam and res"rvoir. <br /> <br /> <br />Test borings were drilled on the crest of the dam and right abutment, and test <br /> <br /> <br />pits were excavated by backhoe in potential borrow areas. Soils were sampled <br /> <br /> <br />from test borings, test pits, and a nearby gravel pit, and were analyzed for a <br /> <br /> <br />variety of properties in the laboratory. Refraction seismic traverses and <br /> <br /> <br />resistivity soundings were performed on the dam crest, and seismic traverses <br /> <br /> <br />were run in a potential borrow area. <br /> <br />The bedrock of the project area chiefly consists of interbedded sandstone, <br /> <br /> <br />shale and thin coal. The overburden soil is principally clay with some silt, <br /> <br /> <br />sand, gravel, cobbles and boulders. The dam embankment also is composed of <br /> <br /> <br />this type of material. Clay (weathered clay shale) separates the embankment <br /> <br /> <br />soils from more resistant, less weathered bedrock. <br /> <br />Core recovery from the test borings was good, and RQD was moderate. <br /> <br /> <br />Bedrock permeability ranged from low to moderately high. Detailed drill logs <br /> <br /> <br />are found in Appendix A. <br /> <br />No critical geologic conditions were identified at the site that would <br /> <br /> <br />preclude the proposed enlargement of the dam and reservoir. A modified <br /> <br /> <br />homogeneous compacted earth embankment would best utilize locally available <br /> <br /> <br />soil materials. The preliminary stability analysis indicates foundation soils <br /> <br /> <br />and bedrock can support an enlarged earth embankment of the proposed height. <br /> <br /> <br />Control of seepage through near-surface bedrock will be necessary to reduce <br /> <br /> <br />destabilizing f~ces in downstream foundation and toe area. This can be <br /> <br /> <br />accomplished with internal and downstream filter drains. Seepage reduction by <br /> <br /> <br />grouting the foundation bedrock will also reduce destabilizing seepage <br /> <br /> <br />pressures. Ample borrow materials may be obtained at the site or from nearby <br /> <br /> <br />sources. Gravel and aggregate materials can be acquired from identified <br /> <br /> <br />sources approximately 4 to 6 miles south of the reservoir. Seismic risk is <br /> <br /> <br />judged to be low to moderate at this site. <br /> <br />-1- <br />