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Mr. Jim Mattern March 19, 2007 Page I S 7. Gd-2 Cut Failure Conditions: Reduce the strength of bedding planes in the mudstone layer above main L-Seam to residual strengths to represent time-dependent softening. This assumption is based on observations of shallow sandstone on the northeast side of the landslide block that were so weak that they formed remnant `crumbly spires.' The rock mass strength of the G-Dip floor material was reduce above the mudstone layer above main L-Seam to residual strengths to represent time-dependent softening due to the landslide block wanting to move in that direction allow the floor to yield. This assumption is consistent with observations of the pit floor which appeared to have heaved or buckled. ~ Compute equilibrium condition. Geometry is same as shown in Figure 7. G-Pit Ground Water Conditions Not much information is known about groundwater conditions immediately prior to the landslide event. Figure 8, which was discussed in the landslide trip report, shows that significant rain fell prior to both the Gs-6 Cut failure of September 2005 and the Gd-2 Box Cut landslide failure of October 2006. There were three major storm events (>0.25 inches) the week before the landslide and one after the initial movement. Groundwater piezometer data suggests that head conditions can vary widely, and this is thought the result of open fractures in sandstone layers and lack of fractures in mudstone layers. Several simplifying assumptions were made in the model to represent worst-case, homogeneous-flow conditions. Water surface in the model is assumed 10 ft below ground, parallel to bedding. The mined pits and spoils were assumed fully drained due to their high porosity. This assumption is based on observations that downdip of the toe pile the drainage ravine had a constant stream of water of about 7-8 gpm shortly after the event. The rock below the phreatic surface was assumed fully saturated and its saturated density based on an average porosity of 0.05. Groundwater flow is not simulated; rather pore water pressures were used only to compute effective stresses. Four water tables were defined in Table 3 to approximate being parallel to the ground surface. The water table planes defming the water pressure gradient in the model are depicted in Figure 9, along with contours of computed pore pressures. A close-up view of pore pressure contours in the vicinity of Gs-6 Cut highwall is shown in Figure 10. The blasted M-Q Interburden rock of Cut 6 is assumed drained and is assumed to have no pore water pressure. Contours of assumed pore water pressures are shown in Figure 11 for only the weak mudstone layer above the main L-Seam since this is the weakest layer in the sequence and is thought to contain the slip plane. G-STRIKE PIT CALIBRATION ANALYSIS The first part of the analysis was to calibrate the material properties to the localized failure that occurred in the Gs-6 Cut highwall in September 2005. Using the best estimated strength properties for the saturated rock mass (referred to as peak strength conditions), displacement contours, shown in Figure 12, indicate the largest movements occur near the Agapito Associates, Inc.