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1 t San Luis Mine Phase Q, Raise 2 Design Repon ' Table 1 presents a summary of the depth to saturated tailings at each of the probe locations as determined from the residual pore pressure data. As shown in this table, the level of tailings saturation increases with increased distance from the embanlonent. For locations approximately 80 ' ft from the crest of Raise 1 ("C" locations), the average depth to saturated tailings is 32.5 ft (approximately 8566.1 ft elevation). For locations 125 ft from the crest of Raise 1 ("B" locations), ' the average depth to saturated tailings is 26.1 ft (approximately 8571.8 ft elevation). For locations 175 ft from the crest of Raise 1 ("A" locations), the average depth to saturated tailings is 22.5 ft (approximately 8574.9 ft elevation). 1 '' TABLE 1 DEPTH TO SATURATED TAILINGS CPT PROBE DEPTH (ft) CPT PROBE DEPTH (ft) lA 17.2 3A1 22.8 1B1 24.9 3A2 24.6 1B2 25.1 3B 27.1 1C > 27.2 3C 31.3 2A1 20.5 4A1 25.9 2A2 21.0 4A2 25.4 2B 25.8 4B 27.4 2C 31.0 4C 35.3 ' Below the initial level of saturation the tailings typically remain saturated but exhibit residual pore pressures which are generally less than hydrostatic. This is due to the underdrain system in the impoundment, and drainage provided by the embanlonent itself, which creates downward seepage gradients. This effect becomes more pronounced with depth. ' As a typical example, Figure 3 presents a plot of residual pore pressure versus depth for CPT-2B. As shown on this figure the residual pore pressures are zero or slightly negative down to a depth of 24.8 ft (7.55 m). At 28.1 ft (8.55 m) a residual pore pressure of 1.0 psi (0.7 m) was recorded ' which would indicate an equivalent static water level of 25.8 ft (7.85 m) and a corresponding line indicating normal hydrostatic pressure below this level is included on the figure. As shown, the tailings down to a depth of 41.2 ft (12.55 m) exhibit near hydrostatic residual pore pressures. Below this depth the tailings exhibit residual pore pressures which deviate increasingly from hydrostatic pressure with depth. ' The dynamic and residual pore pressure data indicates that the tailings are generally contractive ' during shear exhibiting positive excess pore pressures during advance of the probe. However, o Y 2-3 ro~ect o.