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~, and any unbalanced lateral stresses. At the very gentle dip of 2.2 to 3.2 degrees, a high pore-fluid <br />pressure would be necessary to cause the sheaz strength to be less than the sheaz stress. <br />It is very unlikely that sheaz strength along bedding planes in the.coal seam (or seams) mined at <br />Oliver No. 2 could be reduced to this extent because: <br />1. There is no high pre-fluid pressure; the water can drain out the Oliver No. 2 Mine portals <br />even though seals of cinder blocks, arranged in double rows, were constructed 700 to 800 <br />feet south of the portal area. This is evidenced by the lack of spring development in the <br />overburden. <br />2. The dip of bedding is 2 to 3 degrees-much less than the 8 to 17 degree angle of friction for <br />any clays that might be present in the coal-bearing rocks of the Mesaverde Formation. <br />No indication of block glide has been observed in the 42 years since the mine was closed. <br />4. All of the Oliver No. 2 Mine workings are outside the angle of draw of planned B-Seam <br />mining, with the exception of the first Box Canyon panel. <br />5. State Geologists from most coal-producing states were contacted regarding the known <br />occurrence of any block glide in such gently-dipping rocks as in the Oliver No. 2 Mine azea. <br />Not one could recall an occurrence of block glide, including those from eastern states where <br />• coal seams typically overly a soft underclay making block glide more likely (John Rold, <br />Written Communication, November 15, 1996). <br />Block Glide Potential Due to Mining in the B-Seam in ithe Oliver No. 2 Mine Area <br />Block glide due to MCC mining of the B-Seam will not occur iri bedrock beneath the coal zone <br />mined at the Oliver No. 2 Mine. This is based on two factors: (1) these rocks occur beneath the <br />North Fork valley and aze, therefore, laterally constrained; and (2) the B-Seam in this area has a dip <br />angle of 2.6 percent which is less than that of the E/D0. <br />Effects of Rugged Topography on Subsidence and Mirie Stresses <br />The subsidence factor reportedly can vary significantly in draws and on ridges in rugged <br />topography. Gentry and Abel (1978, p. 203-204) report that vertical displacement was 25 to 30 <br />percent greater on a ridge than it was in an adjacent draw in the York Canyon (Raton, New Mexico) <br />longwall mining azea. Based on this information, the subsidence factor is projected to be closer to <br />0.6 in deep draws and closer to 0.8 on isolated ridges in the Box Canyon mining azea. No <br />significant similaz influence is expected in the Apache Rocks rraning area because there aze few, if <br />any, isolated ridges. <br />Based on observafions by Mr. Dunrud in the Somerset Mine in the (rnid-1970s, stresses tended to be <br />• significantly higher beneath isolated ridges than they were beneath more uniform overburden of <br />similaz thickness. For a similaz mine geometry, roof falls, bumps! (rock bursts), and floor heaving <br />2.05-125 March 1005PR11 <br />~-lQ°~ <br />