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studies by Rocky Mountain Geotechnical, Inc. were utilized. The <br />• typical parameters represent peak strength conditions while the <br />conservative parameters represent the observed residual strength <br />conditions. As may be seen from results even utilizing the <br />typical or peal: strength parameters commonly results in factors <br />of safety at or just below 1.0 and confirms the marginally stable <br />to unstable conditions known to exist in these materials. Actual <br />demonstrated shear strength characteristics of these materials <br />are obviously somewhat higher than the measured values on similar <br />slide materials near the portal. A sensitivity analysis on the <br />strength values used for the colluvial material results in the <br />back calculation of a friction angle of 27 degrees for a minimum <br />factor of safety of 1.0 (assumping the measured effective <br />• cohesion to remain constant). <br />8.3 SUBSIDENCE EFFECTS <br />8.3.1 Previous Work <br />Our literature search efforts disclosed no published works on the <br />interaction between subsidence and landsliding. We were, <br />however, able to locate one unpublished report prepared by Mr. A. <br />T. Iannacchione and T.E. Ackman of the U.S. Bureau of Mines, <br />Pits burgh Research Center (internal report number 4571 - <br />"Reactivation of Recent Landslides by Surface Subsidence From <br />Longwall Mining", December 19851. The paper describes the <br />reactivation of two old landslide features located in the Dunkard <br />Basin area in Pennsylvania (northern Appalachians). Reactivation <br />. was associated with the passage of a longwall mining operation <br />23 <br />