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1 ' San Luis Mine Phase n, Raise 2 Design Repott ' instrument is an ideal tool for investigating thinly layered deposits such as tailings. The CPT data includes tip resistance, sleeve friction, and dynamic pore pressure recorded at 5 cm intervals. ' Four CPT probes were conducted on each of four earthen ramps constructed on the beach tailings to provide access in the area of the embankment raise, as shown on Figure 1. The four probes ' conducted at each ramp were located at three separate points; approximately 80, L25 and 175 ft from the upstream crest of the Raise 1 embankment. The forth probe conducted from each ramp was used to "twin" one of the probes at the three locations to provide data on the potential for material ' vaziations over short distances and were situated approximately 5 to 10 ft from the probe being twined. ' The access ramps, and therefore subsurface investigations, were concentrated in the central portion of the embankment to maximize the amount of data at the critical embanlanent section. This area ' also contains the thickest sequence of tailings and should represent the worst case conditions with respect to tailings drainage, consolidation and extent of saturation. ' The CPT test data and interpreted output for each CPT profile are contained in Appendix B.2. Additional CPT data reductions and summaries are contained in Appendix C. The following ' summary of the tailings conditions encountered makes specific references to the data contained in these appendices. ' , 2.2.2 Residual Pore Pressures ' The piezocone CPT probe records the dynamic pore pressures generated during advance of the probe at 5 cm intervals. Pore pressure dissipation data was obtained at one meter intervals in each of the ' CPT profiles as advance of the probe was stopped to add a rod. The dynamic pore pressures are allowed to stabilize when the probe is stopped and the equilibrium or residual pore pressures obtained give the equivalent hydrostatic head in the tailings at each particulaz depth. This data is ' summarized in Appendix C.1. Included in this appendix are select plots of the actual pore pressure dissipation data recorded. Atypical example from CPT-3A2 at a depth of 31.2 ft (9.50 m) is ' included as Figure 2. As shown on this figure, the dynamic pore pressure was equivalent to approximately 7 m of head (10 psi) at the start of the dissipation record and dropped to 1.9 m (2.7 psi) after approximately 65 seconds. ' The pore pressure dissipation data confums that the upper portion of the tailings are unsaturated and ' typically indicates negative residual pore pressures. The presence of negative pore pressures indicates that the unsaturated tailings are frequently overconsolidated as is typical of subaerial methods of deposition and well desiccated tailings. 1 u Y 2-2 ro~ect o. 1