The pressure relief of coal pillars in close-distance multi-coal seam goaf is a complex engineering problem with the characteristics of “dynamic mine pressure”. Hence, this paper studies such problems. First, the influence factors of the coal pillar in the goaf on the mine pressure of the mining face of the lower coal seam under this condition were theoretically analyzed, and it was concluded that vertical stress is the most important element, followed by horizontal stress. Next, a physical similarity simulation experiment was designed to study the stress distribution law of the coal pillar floor in the goaf before and after pressure release and the damage depth. Finally, a technology and monitoring method for coal pillar blasting pressure alleviation in goaf were introduced and implemented in engineering practice. After the pressure is alleviated, the surrounding rock stress of the lower coal seam mining face is redistributed, and the vertical stress is decreased by 20%. The adjacent rock’s deformation is improved. This technology’s cost and safety advantages are extraordinary and helpful for mining coal seams over close distances.
The large-scale mining of coal resources promotes the formation of section coal pillar groups between working faces. The overlying strata are supported by coal pillars, which leads to the formation of a unique fracture-bearing structure in the key stratum, resulting in the evolution of fissures (cracks) and a generally high load on the supports. Studying the fracture-bearing structure formed by coal pillars and overlying strata (fissures) is the basis for realizing rational mining of working faces. Here, the evolution characteristics of coal pillar-overburden rock (fissures) in shallow coal seam mining and the working resistance of the support with stable fracture bearing structure of section coal pillar and overburden rock were studied in the No. 1-2 coal mining of Longhua Coal Mine in Shenmu City, Northern Shaanxi. The fissure evolution characteristics on both sides of the coal pillar and the fracture-bearing structure of the rock stratum were obtained by physical similarity simulation experiment. The mechanical calculation model of the coal pillar-overburden rock (fissure) structure was established by theoretical derivation and calculation, and the working resistance of advanced support with a stable mechanical structure was studied. The research shows that the fracture evolution and rock fracture characteristics of a shallow coal seam mining face can be divided into three zones. Through the reanalysis of the mechanical structure of coal pillar-overburden rock (fissure), the combined mechanical structure of the subkey stratum consisting of a lagging broken step rock beam structure and the main key stratum consisting of a hinged rock beam structure was obtained. Combined with the failure characteristics of the section coal pillar, a mechanical structure calculation method suitable for the bearing characteristics of section coal pillar support in shallow coal buried layers was obtained, and the field measurement results were verified.
The thin spray-on liner is an inorganic polymer product that has been widely used to support mine perimeter rock roadways, but it is mainly used in metallic hard rock roadways with high rock strength and is less used in roadways affected by roadway corrosion and weathering in shallowly buried coal seams. Therefore, this study studies the thin spray-on liner support technology under such geological conditions. First, the causes of anchor support failure in this condition are analyzed, and it is concluded that alkaline ionized water corrodes the anchor rods, and chloride ions in the water play a role in accelerating the degree of anchor rod corrosion. Next, microscopic testing was used to determine the content of weathering and swelling minerals contained in the roof rock and the development of tectonic fissures. Third, the loosening circle of the surrounding rock is theoretically calculated and used as a basis to design the anchor mesh rope support parameters for the roadway. Finally, the construction process of a thin spray-on liner anticorrosion and antiweathering support technology is introduced. This technology improves the anchor force environment of anchor rods while incorporating anchor rods (ropes)—rock—metal mesh into the support system to play a coupling support role. On-site monitoring is performed to derive the optimum thickness of the spraying layer in different environments. At the same time, the deformation of the roadway surrounding rock and the anchor force can be improved to meet the requirements of anticorrosion and antiweathering and tighten the roadway surrounding rock. Compared with concrete support technology, the economic and environmental benefits of this support technology are apparent, and it helps to promote the application in shallowly buried coal seam mines.
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