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1 1 u 1 1 1 San Luis Mine -Phase U, Raise 1 Design Report are presented in Appendix A.2. Visual observation of the tailings retrieved indicates that deposition has resulted in complex layers consisting of various mixtures of tailings sand and slimes. Samples collected from the borings were saved for laboratory testing. Physical testing consisted of grain size analyses, Atterburg Limits and triaxial shear. The grain size analyses, which are included in Appendix A.3, indicate that the whole tailings consist of approximately 60 percent by weight which is finer than a No. 200 sieve (0.T4mm). Grain size analyses of relatively sandy tailings indicate that 40 to 50 percent of this materiaB is finer than a No. 200 sieve. Grain size analyses of the finer grained tailings ("slimes") indicate that 65 to 80 percent of this material is Finer than a No. 200 sieve. A sample of tailings slimes submntted for Atterburg Limit determination resulted in liquid limit of 23.8 and no plastic limit (i.e. non-plastic). A similaz sample of tailings slimes was subjected to a 3-point consolidated-undr3ined triaxial shear strength test. Test specimens consisted of re-molded tailings samples which were placed in the triaxial cell at approximately 80 pcf, saturated and then consolidated under lgads equivalent to roughly 25, 55 and 90 feet of tailings (or slightly less tailings and embankment fill). Shearing was conducted under undrained conditions with pore pressure measurements recorded. In terms of effective stresses, the Mohr-Coloumb shear strength parameters at 5 percent strain are a friction angle of 31 ° and 358 psf cohesion. For a strain of 10 percent, the strength is slightly higher with a friction angle of 32° and 486 psf cohesion. The results of all laboratory testing aze contained in Appendix A.3. 2.2 Cone Penetrometer Testing During May 1993 a series of six CPT probes were conducted in the tailings which will underlie the ' embankment raise. The CPT probes were conducted by Terra Technologies -Southwest Inc of Houston, Texas using a piezocone CPT probe. This type of instrument provides a continuous read- ' out of pore pressures generated at the tip of the cone as it is advanced and is capable of measuring pore pressure dissipation when the cone is at rest. The data obtained from the physical sampling programs was utilized to calibrate the CPT results during the data reduction process. Interpretation of the CPT results confirms that the complex ' layering observed in the shallow hand auger borings continues with depth. The pare pressure data indicates that very little, if any, of the tailings penetrated are saturated, particularly those at the northern CPT locations (Figure B-1 in Appendix B shows the CPT probe locations). However, a minor spike in the pore pressure printout was noted over depths of approximateffy 14 to 18 feet July 13, 1993 3 SRK Project No. 14719 I~