Thin Bedrock Coal Seam Overlying Rock Failure Mechanism under the Influence of the Depositional Environment
Feng Du and Haibo Bai
State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology, Xuzhou 221008, China
Taking Bai-shan coal mine and Yu-yang coal mine as research base, this paper systematically focus on the microstructure and mechanical characteristics of overburden strata, time and space process of overburden strata movement in the shallow seam under thin base rock under different sedimentary environment. The result indicates: In the coal measures of Carboniferous and Permian under seashore and shallow sea, the major mineral constituents of overburden in the shallow seam under thin base rock are weathered mud stone and sandstone, mechanical properties of rock are all depressed, such as compression strength sigma c and deformation modulus E , rock particles contain large numbers of clay mineral , as the kaolinite and goeschwitzite, in the deposition water environment, the rock will be easy to have the plastic deformation and the rock's mechanical properties will reduce further , rock is broken by the plastic failure primarily and rock breaking is good to cut off the water performance. When on covers the rock layer broke it is easy to form loose body arches the balanced structure; But the Jurassic Period coal formation stratum in the lakeside delta environment of deposition, on the thin bedrock shallow submersion coal bed covers the rock layer the mineral ingredient mainly by the mudstone and the sandstone primarily, but mudstone compressive strength sigma c, the modulus of deformation E equipollent study nature is higher than the sandstone, the intensity of mudstone stronger than sandstone on the main production seam; the porosity, moisture content and tensile compression ratio of sandstone is great; the clay soil content of mudstone and sandstone is low. So it has new damage and excursion character of canonical brittleness, the feebleness capability of resist remolding and the feebleness revival capability of water-stop. It settled the character of dynamic vary of height in breaking of overlying strata in shallow coal seam with a thin bedrock as elements fitting based, and put forward long-wall mining to control blowing out Water and bursting sand. The technique was applied in Yu-yang colliery successful and put into green technical conservation water of mining, because of the hard formation existence on covers the rock layer breaking is easy to form the key stratum balanced structure. The findings regarding instructed the two Huais newly developed area and northwest local thin bedrock shallow submersion coal bed realization green mining have provided the theory support.
Keywords: shallow coal seam with thin bedrock; sedimentary environment; loosed arch; key stratum; law of evolution
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