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<br />' San Luis Mine Phase II, Raise 2 Design Repott <br />' 2.0 TAILINGS INVESTIGATIONS <br />2.1 Insitu Density <br />' During April 1995, a series of 12 measurements were conducted to determine the insitu density of <br />' near surface tailings in the tailings beach area adjacent to the existing embartlattent. These <br />measurements were obtained from the tailings within one ft of the tailings surfacc by nuclear density <br />gauge. <br />The tailings beach, which will support the upstream portion of the raise, was found to have an insitu <br />' dry density which ranged from 85.1 pcf to 99.3 pcf with a weighted average of 95.0 pcf. These <br />values are higher than the density which was assumed for freshly deposited tailings in the <br />Amendment and are higher than the tailings beach densities measured in conjunction with the Raise <br />' 1 investigations (81.4 to 90.6 pcf, 85.5 pcf average}. This increased density is attributed to a <br />greater degree of desiccation associated with the tailings investigated during the current study due <br />' to a slower rate of rise as the impoundment fills. Insitu density test results are included in Appendix <br />B.I. <br />' The overall average tailings density has also been calculated by comparing prodluction records with <br />a survey of the impoundment volume. The tailings impoundment was surveyed on May 19, 1995 <br />and June 9, 1995. These surveys result in a tailings volume of approximately 117.5 million cubic <br />' ~ ft. As of June 1, 1995 total production is estimated at 5.83 million tons. This results in an average <br />tailings density of 99.2 pcf and indicates that the tailings are consolidating well as the tailings depth <br />' increases. All data collected at depth and presented in the Reclamation Evaluation support this <br />conclusion. <br />' 2.2 Cone Penetrometer Testing <br />' 2.2.1 General <br />' During April and May 1995 a series of sixteen CPT probes were conducted in the tailings which <br />will underlie the embankment raise. The CPT probes were conducted by Cone'Pec, Inc. of Denver, <br />Colorado using a piezocone CPT probe. This type of instrument provides a continuous read-out of <br />' pore pressures generated at the tip of the cone as it is advanced and is capable of measuring pore <br />pressure dissipation when the cone is at rest. The cone system records data on 5 cm intervals, thus <br />' providing much greater resolution than conventional soil borings and the ability to detect much <br />thinner layers of greater or lesser strength than the surrounding material. Due to the greater <br />resolution of strata variations and pore pressure measurement capabilities, the piezocone CPT <br />1 <br />u y Z_t ro~ect o. <br />