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1 <br />San Luis Project -Phase 11 Raise t Expansion Cosutruction Statue Report <br />' function of the facility. Subsequent permeability testing of both the embankment fill and tailings <br />has demonstrated that the fill is more permeable that the bulk of the tailings and will not impede <br />drainage from the tailings. <br />The approved permit documents require ongoing testing of the tailings deposition characteristics <br />' and submittal of a design document confirming the proposed upstream raise for Phase II, Raise <br />2 prior to commencement of Raise 2 conswction. <br />' Direct shear testing of samples of the raise embankment fill which were prepared to replicate <br />actual field conditions resulted in sheaz strengths which exceed those utilized in the stability <br />' analyses presented in the design report. Therefore, the material which has been used for the <br />raise construction will result in an increase in the stability of the structure. <br />6.4 Material Type 2 -Liner Cover/Draiaage Blanket <br />' Revising the gradation specifications for material Type 2 to allow for variation in the mid range <br />of the material gradations will not affect the function of the facility. The drainage pipes aze <br />' fully enclosed in filter fabric, thus no filter criteria for the coarse fraction in the Type 2 material <br />exists. The gradation specified for the Type 2 material primarily considered the filter <br />' requirements for preventing large amounts of tailings from passing through the drain layer and <br />blinding off the drain pipes. The tailings slimes, which aze the primary concern with respect <br />' to the drain pipes, have a d~ which may range from approximately .03mm to .04mm or perhaps <br />even smaller. Following the Corps of Engineers filter criteria, the drain layer is then required <br />to have a d,o which is less than .75 - .25mm. Using a well graded material for the filter results <br />' in approximately 0-30 percent which will be finer than a iY200 sieve (0.74mm). In case drain <br />material which has fewer fines is overlain by tailings slimes, some migration of the tailings into <br />' the drain layer will occur and a "naturally" graded, zoned filter will develop as long as massive <br />tailings migration or piping does not occur. To prevent large scale piping,, the Corps of <br />Engineers filter criteria suggests that the d,s of the drain should be less than 5 times the des of <br />the tailings slimes or approximately .5 - .4mm. The specifications require a minimum of 25 <br />percent finer than a 1140 sieve (.42mm) therefore this criteria is met with the material specified. <br />' Although not evident in the gradation for Type 2 material, occasional oversized particles have <br />been observed in the material as i[ is placed on the liner. The larger oversized particles are <br />removed during the QA/QC visual observation implemented by the Owner and placed on top of <br />' October. 1993 ,g SRK Ptojtxt No. 14725 <br />