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M03106GE <br />changes to the calculated theoretical factor of safety indicating <br />that the stability analysis was sensitive to slight variances in <br />the soil strength characteristics of the coal gob. Because the <br />actual gob material to be placed in the pile is not yet being <br />produced we recommend that laboratory strength tests of the coal <br />gob material be conducted at the beginning of coal gob production <br />and periodically during the construction of the coal gob pile to <br />verify the assumptions made during our stability analysis. We <br />suggest that laboratory strength tests be conducted on the coal gob <br />material during placement about every ten (10) feet of gob fill <br />height or about twice per year, whichever occurs more frequently, <br />to verify that the material characteristics and strength do not <br />vary significantly, with time and mined material changes, from <br />those assumed in our analysis. We-are available to discuss this <br />with you. <br />Our stability analysis was performed along a proposed cross <br />section of the gob pile site as shown on Figure 1 by J.E. Stover <br />and Associates. The proposed cross section provided was located at <br />or near the maximum height of the proposed gob pile fill. The <br />stability analysis of the proposed cross section indicated a <br />theoretical calculated factor of safety ranging from about 1.5 to <br />about 1.8 depending on the gob strength characteristics used. The <br />theoretical calculated factors of safety were 1.5 which were <br />associated with the strength characteristics of the existing mine <br />gob and a theoretical calculated factor of safety of 1.8 associated <br />with the estimated strength characteristics of other wash plant gob <br />materials. The slope stability analysis for the proposed gob pile <br />is presented on Figures 5 through 8. <br />Our stability analysis of the top soil and cover material stock <br />piles were performed along a proposed cross. section of each of the <br />proposed stock pile sites as shown on Figure 1 by J.E. Stover and <br />Associates. The proposed cross sections provided were located at <br />or near the maximum height of the proposed topsoil and cover <br />material stock pile fills. The stability analysis of the proposed <br />cross sections indicated a theoretical calculated factor of safety <br />greater than 1.5 for each proposed stock pile. The stability <br />analysis for the proposed top soil and cover material stock piles <br />are presented on Figures 9 and 10. <br />4.4 Earth Work <br />It is our opinion that the materials for the gob pile and the top <br />soil and cover stock piles should be placed at or wet of optimum . <br />moisture content for compaction. The material should be placed in <br />thin lifts of uniform thickness and compacted to at least ninety <br />(90) percent of the maximum dry density as defined by ASTM D698, <br />standard moisture density relationship (Proctor) test. <br />I~ <br />7 <br />~Cam6ert ana ~,o~'ociateo <br />CONSULTING GEOTEOM NICAL ENGINEERS ANO <br />MATERIAL TESTING <br />