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Ms. Christine Johnston <br />Mountain Coal Company -~• <br />August 8, 1996 <br />Herding Leweon Assodetee <br />3 , <br />procedure to calculate the factor of safety against failure. The input information for the analyses includes, but is <br />not limited to, slope geometry, groundwater conditions, soil strengths, and earthquake loading conditions. <br />CONCLUSION <br />The perched water table slope stability analyses was conducted on the 24 previously submitted slope stability LRP <br />profiles. The current analyses involved evaluating the effects of a perched water table on the previously submitted <br />slope stability models. The minimum factor of safety for the LRP with a perched water table is 1.45 on Profde 3 - <br />10%coal fines (see Table One). <br />The stability of the LRP, with a perched water table, during an earhquake event was also investigated using an <br />assumed maximum horizontal and vertical ground acceleration of 0.1 g (earthquake loading factors). The minimum <br />psuedostatic factor of safety analysis was found to be 1.17 for Profile 3 - 10% coal fines. This factor of safety <br />(F.S =1.17) is above the minimum design factor of safety (F.S =1.0) for earthquakes. Critical failure circles and thew <br />associated factors of safety can be found in the attachments. <br />The 1.45 factor of safety for Profile 3 @ 10% fines does not meet the regulatory requ'vements of DMG. The <br />minimum accepted faMOr of safety for slopes utilizing coal refuse as a building material is 1.5. During periods of dry <br />field conditions the factor of safety for Profile 3 climbs to 1.75 (as outlined in Table One). It is FII,A's opinion, <br />based on long term working and monitoring experience (From July, 1981 through July 1996) with the Lower Refine <br />Pile project that the 1.45 factor of safety is within the margins of tolerance for non-failure of the slopes at the LRP. <br />As of August 7, 1996, the WEM completed construction of a french drain along the base of the Profile 3 slope (see <br />Figure One). The french drain has a total length of 250 feet with piezometer GB-l as the approximate center. HI.A <br />recommends long term monitoring of the french drain outlet, piezometer GB-1, and monitoring well GP-lA at the <br />base of the LRP/Profile 3 east flank. The close proximity of the piezometer to Profile 3 and the french drain outlet <br />allows for an accurate long term review of the water levels in this area. if monitoring of the piezometer and the <br />french drain outlet indicates increasing water levels, WEM may wish to establish a permanent set of slope stability <br />markers to monitor potential movement of the slope. By monitoring potential slope movement, mitigation measures <br />may be implemented prior to any mass movement of the slope. <br />If you have questions or requ'Ire more information, please call me at (801) 363-0455. <br />Sincerely <br />IiARDING LAWSON ASSOCIATES <br />~~~ <br />Loren A. Jalber, P.G. <br />Project Eng' eri y` <br />Charlie C. Rahn, P.E. <br />Principal Engineer <br />LAl/cn <br />Attachments <br />G.~p°let9'afk194Wpruc dx <br />