2001-12-11_PERMIT FILE - C1980007A (2)

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April 1989 ,- 3.4.A.4 Geotechnical Analyses and Desiyn_.~_&_~ Seams Geotechnical analyses and design work was done in preparation for mining the B seam as well as to look at potential for multiple seam mitring. The geotechnical work also preliminarily addressed seam mining order, i.e. ascending vs. descending, for areas not currently in the 5 year permit mine plan. The scope of geotechnical work done includes the following: ° Review available geotechnical data to establish geotechnical framework for the analyses and design. ° Perform additional laboratory mechanical property testing to develop an adequate data base for the design and analyses. ° Develop a geotechnical design for room and pillar and longwall mining. ° Evaluate surface subsidence based on calculations of five subsidence profiles tltrot[gh key cross-sections of the property to assess the impact of subsidence to the surface and ' features. The basis of the work presented herein is a geotechnical study performed by .J.F.T Agapi.to and Associates, consulting geotechnical and mining engineers. Geotechnical Framework GROUND COTIDITIONS Itt the Somerset coalfield, five seams have been mined that are located near tl~e base of the Mesa Verde Formation. Figure 3.4.A.1.A is a stratigrapltic sect.i.on showing tl~e location rif the seams and strata types wlticlt consist mostly of interbeddesandstones. West Allc Coal Company is present:l.y mining in the F Seam in the Mt. Gunnison property. This study considers mining this seam, as well as t}te E and B Seams. The regional dip in the Mt. Gunnison property is three to five degrees to the N-NE, attd the strata have been gently folded into a plugging syncline. Major joint systems trend NW-SE and NE-SW with minor systems in a N-S and E-W orientation. The dip of the joi.ttts is always ricer vertical. No major faulting has beets detected in the property.