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~~. <br />~~ <br />~~ <br />ii~ <br />1~ <br />~~ <br />~~~ <br />~p <br />!~ <br />~~ <br />~~ <br />~~ <br />~ii <br />!~ <br />~~ <br />~~ <br />'J <br />_~ <br /> <br /> <br />Woodward-Clyde <br />Corasultart+ts <br />3.0 <br />STABILITY~-NALYSES <br />3.1 GENERAL <br />Three series of slope stability evaluations were performed to evaluate the stability of <br />Dam No. 1. The first series of stability calculations were made to evaluate the stability <br />of the existing height dam with the phreatic levels based on recent piezometerr readings. <br />The other two series of stability calculations were performed to establish thre~~hold levels <br />for piezometers, first for the existing height dam, then for the dam rain;d to crest <br />Elevation 8900. The stability of the embank®ent at each of the five study sections was <br />examined in each of the three series of stability calculations. As described in this report, <br />slope stability analyses made for the existing height dam are intended not only to <br />evaluate the stability of the existing embanltznent, but also to provide a baseline from <br />which Henderson Mill personnel can examine the stability of Dam No. 1 as it is raised. <br />Slope stability analyses were performed using the computer program "UTEXAS3". <br />Spencer's procedure of slices was used for computing the theoretical factors of safety. <br />An automated seazch for circulaz azcs with low factors of safety was used for the <br />analyses. Material properties assumed for the stability analyses aze based on data from <br />prior investigations. <br />3.2 INPUT TO ANALYSIS <br />3.2.1 Cross Section Geometry <br />The external geometry at each of the five study sections was constructed usutg recently <br />obtained site topography, based on serial photographs taken November 19, 1991. The <br />location of the five study sections including existing piezometers at each study section <br />arc shown on Figure 1. The internal geometry of the tailing embankment was <br />established based on information available from previous studies, and primarily tailing <br />profile sampling work. Tailing surface sampling work including profile sampling <br />accomplished in 1980; 1988; and 1989 is summarized in our "Evaluation of Tailing Grind <br />arvvRU oam-sverr 3-1 <br />