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15 <br />^ 3.4 PIINING BELOW FUTURE WASTE ROCK PILE <br /> Little is known at present about mining below the area <br /> of the proposed waste rock pile. It has to be expected that <br />' any mining method will cause the disturbance of the over- <br /> burden above the F coal seam by subsidence. This, in turn, <br /> will cause the deterioration of physical properties of the <br /> overburden rock. The disturbance will probably be proportional <br />' to the amount of the subsidence. If longwall mining methods <br /> are to be used below the proposed waste rock pile, subsidence <br />' on the order of several feet could be expected and consider- <br /> able deterioration of physical properties would result. If the <br /> room and pillar method is used with pillars left permanently <br />' in place, or if mining below the proposed waste rock pile is <br /> to be eliminated, the disturbance could be very limited. On <br />' the other hand, subsidence may cause increased permeability <br /> of the overlying rock and it may enhance natural drainage of <br />' the area. <br />' 4.0 STABILITY ANALYSES <br />' <br /> 4.1 GENERAL APPROACH <br />' <br /> As was discussed earlier, there are not sufficient data <br /> available for detailed stability analyses of the slope below <br />' the upper bench and for the evaluation of the influence of the <br /> upper waste rock pile. <br /> <br /> It has been our experience, however, that even stability <br />' analyses using an incomplete set of data can provide valuable.. <br /> information for engineering purposes and they can greatly im- <br />1 <br /> <br /> c[aNroaocoNw~nHC.iNC. <br />