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<br />San Luia Project - Phe.+e II Raue I P.xpsneion ConaWCtion Status Report <br />' original design analyses. This positively demonstrates that the Type 2 material on the upstream <br />face of the embankment is not inhibiting the removal of water from the beach tailings. <br />Utilization of the Type 1 material as originally specified for the dam raise was primarily <br />predicated on the assumption of material availability, It was anticipated that the use of this <br />material in the raise would allow for some migration of tailings into the fill as the Type 1 fill <br />and tailings are not filter compatible. The net result would be to, in effect, increase the fines <br />' content of the fill. <br />In terms of filter compatibility with the tailings, the Corps of Engineers guidelines for filter <br />' design presented in EM 1110-2-2300, Earth and Rack-Fill Dams -General Design and <br />Construction Considerations, recommend that in order to assure that the filter material is much <br />' more permeable than the material to be drained, the 15 percent size (d,s) of the filter should be <br />greater than or equal to 5 times the d,s of the material to be drained, The San Luis tailings have <br />' a d„ of approximately .004 -.006mm which results in a minimum tits for the filter which is .02 - <br />.03mm. Utilizing a well graded filter, the percent finer than a ;4'200 sieve (.07Wmm) should be <br />approximately 35 to 40 percent to assure adequate drainage. The material adopted for use in <br />' the raise fill contains fewer fines than this and therefore appeared to represent a material which <br />would provide adequate drainage. <br />' Furthermore, the raise fill material is fairly dry and will draw moisture out of the tailings due <br />to capillary tension. As this occurs, the tailings in contact with the fill will consolidate quickly <br />and should exhibit permeabilities towards the lower end of the range found to occur in the <br />tailings. The raise fill material has a higher permeability than that of the adjacent tailings and <br />thus will not inhibit drainage from the tailings. Laboratory testing of the raise fill material <br />conducted during preparation of this document on samples duplicating Reld conditions <br />demonstrates that the embankment fill has a higher permeability than the permeability test results <br />which have been obtained in the tailings. <br />' Based on the slow rate of rise and degree of desiccation currently associated with tailings <br />deposition at the facility, the demonstrated ability of the similar Type 2 material incorporated <br />in the upstream face of the Phase I embankment to allow drainage from the beach tailings, the <br />Corps of Engineers criteria for drain materials and the tailings migration into the raise fill which <br />' would have occurred, it was determined that the use of material with a fines content similar to <br />the Type 2 material would be suitable for raise construction and would not altdr the intended <br />' October, 1993 t7 SRK Project No. 14TLS <br />