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i. <br />f <br />~~ <br />_~ <br />~, <br />!~ <br />i ~~ <br />~~ <br />!~ <br />~.~ <br />~~ <br />~I. <br />~~ <br />~~ <br />L' <br />~~ <br />;~ <br /> <br /> <br />WOOdIW8K1-Clyd@ <br />CiORSU~el11t5 <br />4.0 <br />CONCLUSIONS AND RECOMMENDATIONS <br />1. Theoretical factors of safety calculated for existing Dam No. 1 at the 5ve <br />established study sections based on the February 1992 phreatic le~+els and <br />assuming hydrostatic conditions are consistent with commonly accepted <br />engineering practice. <br />2. Threshold elevation levels summarized on Table 2 have been established for <br />comparison to piezometer water level elevations. The threshold level for each <br />piezometer is 10 feet below the ground surface at that piezometl;r. The <br />theoretical factors of safety for the existing embanlortent and for the embankment <br />raised to crest Elevation 8900 with the phreatic surface at the threshold levels <br />were calculated and for all cases analyzed was found to be greater than 1.5. <br />3. Various assumptions have been made in performing stability analyses of Dam <br />No. 1. Each of these assumptions should be confirmed and evaluated as Dam No. <br />1 is raised. Additional piezometers should be installed at about 25-foa~t vertical <br />spacings along the existing study sections as the dam is raised. piezometers in <br />addition to those installed at the study sections may be appropriate to monitor <br />specific azeas of the dam. <br />4. At the time of the next piezometer installation and tailing sampling work, we <br />recommend that tailing samples be obtained and tested to establish tlndrained <br />strength properties, and that the stability of the embanlmtent be evaluated using <br />undrained strength chazacterization for the tailing materials. <br />5. We recommend that Henderson Mill personnel contact WCC immt:diately if <br />there is any unusual behavior observed with the piezometer water levels or if the <br />results of slope stability calculations appear unusual in any way. It is often <br />difficult to evaluate the significance of piezometer water level fluctuations and the <br />impact these have on the overall stability of tailing dams. We would be pleased <br />to assist you in this regazd at any time. <br />1799VRIA Ob03.7LtF1' <br />41 <br />