Laserfiche WebLink
• 2.0 Characterization of Landslide <br />The landslide is characterized as adeep-seated failure mass of colluvium (about 30 to 50 feet deep) <br />encompassing an area of about 40 acres (over 2.4 million cubic yards of earth). The major failure <br />plane is occurring along a relatively flat (about 3 degrees) slickenside clayey material. This is <br />consistent with the geomorphology of the area which indicates that the landslide material is from <br />historic landslides into the historic North Fork Gunnison River. The alluvial deposits from the <br />historic North Fork Gunnison River are beneath the colluvium. Figure 2 is a cross section of the <br />landslide near the substation area which illustrates the geological stratigraphy. <br />Changes in the rate of landslide movement were triggered by wet conditions. Wet conditions are <br />illustrated on Figure 2 6y high water levels within the landslide mass. During wet periods, <br />usually in the spring ,the rate of movement increases, and this is illustrated on Figure 3. The <br />primary cause of wet conditions is from near surface groundwater sources near the head of the <br />landslide and infiltration through tension cracks within the landslide (and previously from <br />sedimentation ponds on the lower portion of the landslide). Wet conditions also occurred as a <br />• result of operational issues, such as broken water mains, uncapped French drains, and surface <br />runoff ditches concentrating flow, however, most of these have been corrected. <br />The current average rate of movement as of April 1998, as shown on Figure 3, is about 0.0005 feet <br />per day at the toe and about .Ol feet per day at the head, which classifies this as a Landslide <br />Velocity Class 2 (LVC-2), and approaching LVC-1 at the toe. This may be described as very slow <br />movement, in accordance with the landslide velocity classification presented in Appendix A The <br />landslide appears to have a constant background movement rate of less than .001 tUday based on <br />Monitoring Point 17 at the toe, which is apparently outside of the landslide area. This could be <br />the result of plastic-viscous flow within the colluvium or shale bedrock or possibly subsidence of <br />the Bear Mine workings in the C seam below the landslide. <br />C~ <br />os2so24\58ss1-vABM <br />