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© MONTGOMERY WATSON <br />• <br />November 3, 2000 <br />Karl Koehler <br />Trapper Mining, Inc. <br />PO Box 187 <br />Craig, CO 81626 <br />1tE: East Flume Pond - As-Built Slope Stability Analysis <br />Dear Karl, <br />This letter report details the results of the as-built slope stability analysis performed on the <br />East Flume Pond Embankment Dam. Included in this report is a summary of the soil properties of <br />the material sampled from the keyway and borrow source during construction, and the stability <br />analysis performed on the as-built East Flume Embankment cross section. <br />1. Soil Characterization <br />• <br />During construction of the East Flume Pond Embankment Dam Montgomery Watson <br />completed a geotechnical investigation of the azea. The geotechnical investigation included <br />disturbed and Shelby tube sampling of the bottom of the keyway and disturbed sampling of the <br />borrow material. According to the laboratory testing of these samples, the USCS classification of <br />the foundation (keyway) material appears to be CL (low plasticity clay with some sands) and the <br />classification of the borrow material used to construct the dam is SC (clayey sand). <br />Tests for Atterberg limits, grain size distribution, specific gravity, and standard proctor <br />compaction were also performed on the soil samples. The results of all the soil testing are <br />included in the attachments to this letter report. To determine the strength properties of the <br />foundation material the Shelby tube samples (taken from the keyway) were subjected to triaxial <br />testing. As shown on Table 1, effective strength parameters for the East Flume Keyway material <br />aze intemal friction angle 33.4° and cohesion of 14.4 psf. To determine the strength properties of <br />the borrow material the sample was compacted to 90% of standard proctor density and subjected <br />to triaxial testing. The material that the compacted embankment at the East Flume site is <br />constructed of has an intemal angel of friction of 29.7° and cohesion of 72 psf. The values of wet <br />unit weight utilized for the compacted and existing conditions are 117.5 pcf and 102.5 pcf, <br />respectively. <br />- , . - TABLE 1 - <br />- <br />INDER AND STRENGTR PROPERTIES OF SODS FOR PONDS <br />°'~ <br />- '~ EFFECTPYE. <br /> ATTERBERG PARTICLESIZE'_ EFFECTIVE ~ CO~S[ON <br />SAMPLE' LBNT15 ' ; ''}: DATA FRICTION ANGLE, <br /> (LL - P[) (9fo passing Na 2011) ~ (Pg~ <br />East Flume Bortow 29 - 71 50 29.7 72 <br />East Rume Ke wa 32 - 16 56 33.4 74.4 <br />• <br />Ifi5 South Union Blvd. Tel' 303 7fi3 5140 <br />Suite 410 Fax: 303 7fi3 8003 <br />Lakewood, Colorado <br />80228 <br />`v1R-/7$' DEC 21 2000 <br />Ser v~ng the World's Environmental Needs <br />