Stress Redistribution Law Of Floor Strata Under Chain Pillar And Its Application In Multi-seam Mining

Multi-seam longwall mining is considered to be the future method of excavating the underground coal in most of the coal countries, such as China and Australia. As upper seam was mined out, chain pillars were left generating severe interaction to the floor strata and the lower coal seam mining, especially for the ultra-close seam mining. This paper presents detailed research on the stress redistribution of the floor strata under the chain pillar of multiseam longwall mining with the methodology of field investigation, analytical derivation, laboratory test, numerical simulation and industrial implementation. The maximum principal stress and the maximum shear stress were employed to evaluate the stress redistribution patterns of the floor strata under the chain pillar, which were also described by the vertical stress and horizontal stress. Two original definitions of the stress threshold contour and interburden-to-overburden were put forward according to the nondimensionalize analysis method. Considering the strata attribute(rock properties, dip angle of coal seam and interburden thickness), the strata stress state(the lateral stress coefficient and depth of the upper coal seam) and the man-made influence( the coal pillar width and mining height) in this reserach, the stress interaction and redistribution of the floor strata under the upper pillar was studied detailedly. The conclusions can provide theoretical framework of a design overview and practical basis for similar mining conditions in other coalfields.