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Evacuation of Bear No. 3 Mine Landslide <br />evidence of uplift or horizontal compression at the toe such as one would expect from a large <br />rotational slide with swell-developed slip plane. Therefore, differential movement in the middle <br />and lower portions of the slide would not be along a defined slip plane, but as diffused <br />interparticulate movement. This could be visualized as much like the diffused movement of the <br />sand within a sandbag as the bag is deformed. The approximately 10-degree steepening of the <br />slope during sliding would indicate a dilation or outwazd swelling of the middle portion of the <br />slide (Section 1, Figure 8). <br />The extension of the slide onto the graded coal slope appears to be due to an accumulation of <br />material which has rolled or slid down from the raveling slope above. We saw no indication that <br />the slide mass had been pushed out or slid over the graded coal surface. <br />Dr. Jim Pendleton, during a recent technical meeting of CDMG, MCC, and WWE personnel <br />raised the question that the November 1997 slide might be a possible indication of a much larger <br />megaslide involving a large portion of the mountain. We have evaluated this possibility and <br />studied the July 14, 1997 aerial photography. Although numerous landslides occur high on the <br />mountain slopes above the November slide (Figure 1), we saw no evidence of the postulated <br />megaslide. If such a slide had occurred prior to the Bear mine closure and extended to depth, it <br />would have disrupted and been noticed in the mine workings. None of the previous investigators <br />have interpreted a megaslide in the area. <br />Rocky Mountain Geotechnical (1986) conducted a stability evaluation of the possibility of a <br />major deep block glide. Their work, which has been reevaluated by Jubenville, concluded that <br />such a slide was highly unlikely. They also concluded that the possibility of a slide large enough <br />to block the river and cause damage to the Town of Somerset, the highway, railroad, or upriver <br />facilities was highly unlikely. <br />831-032.411 Wright Water Engineers, Inc. Page 8 <br />