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Mr. Jim Mattern March 19, 2007 Page 42 envelop failure occurs, as in the case of the red dotted circle for the weaker seam above L-Seam failure is predicted. Given the above discussion on predicted conditions and failure mechanism, it is possible to estimate the limits of failure from the model. By viewing Figure 29 of the velocity and plasticity indicators in plan view, as shown to scale in Figure 31 on H-I2 Interburden sandstone layer, an overlay of both the predicted landslide limits and the actual mapped limits of the landslide can be compared. Figure 32 shows the limits of the landslide superimposed on the aerial photo of the landslide. These results suggest good agreement with the observed failure given the assumed groundwater and weak mudstone seam strength conditions. This means that the calibrated rock mass properties and assumed ground conditions accurately predict the unstable slope condition in the G-Pit area. These properties and conditions can be extrapolated to other areas of the mine to examine potential unstable slope conditions. DISCUSSION The model did simulate the buttressing of the spoils at the toe of the slope. In the field, the toe material was piled 70-120 ft high as a result the landslide block plowing the buttress spoils It was not possible to simulate this behavior with the existing model because it is constrained to small displacements. Similarly, it was not possible to simulate the main 400-ft- wide, tensile-release escarpment zone at the top of the hill, although tensile failure is predicted. For this reason, it is not possible to compare predicted displacements to observed surface cracking without running the model for many more cycles. The issue of predicting the limits of failure to the southwest is difficult to quantify. The white line in Figure 31 was arbitrarily placed beyond the crestline of the hill at the weak mudstone seam outcrop line. Tension cracks in the field extended over the ridgeline into the oak shrubs and the northwest orientation of cracks aligned with the exposed fractures in the sandstone. The most southwestern limits of the hill, where the power pole is located, geometrically forma `nose.' The model does predict failure of the H-I2 Interburden sandstone layer in this region, but the velocities are quite small. The results are interpreted to be stable in this area. No cracks were observed in the field within 200 ft of the power poles, which is where the white line is located in Figure 31. The model is not capable of examining whether cracking might continue toward the power poles without additional assumptions including better information on weak mudstone seam properties, removal of downdip failed material, and verification of pore pressure conditions. The importance of fracture orientation was examined. This was done by rotating the stress tensor for each zone into the orientation of dominant fracture sets and computing the normal and shear stress that would exist on fractures had they been discretely included in the model. The potential for slip is quantified as a safety factor against slip-slip occurs wherever the safety factor is less than 1.0. The safety factor for joints in the primary fracture set hl G-Pit (Strike = N38°W, Dip = 89°N, 0.62 ff) is shown in Figure 33 for the I1-I2 Interbed sandstone layer above the slip plane. The same is shown for the joints in the secondary set (Strike = Agapito Associates, Inc.