Abstract
The study of the effects of mining height on overlying strata movement and underground pressure characteristics during extremely thick coal seam fully mechanized sublevel caving mining is very important for choosing the reasonable mining height and the support. Based on the geological setting and mining conditions at the Xiegou Coal Mine, the results of the physical simulation test and the numerical simulation technology will be used. Some conclusions can be drawn as follows: (1) With the mining height increase, the top coal gradually converted from tensile failure to shear damage, and the coal wall gradually transformed from shear failure to tensile damage. (2) When the mining height is 7.5 m, the full-seam collapse distance, the immediate first weighting interval, and the main roof first weighting length are shorter than that when the mining height is 4m, and the periodic weighting length for the two mining heights is almost the same. (3) With mining height increase, the initial mining stage and the transition stage become shorter, and the production rates become better. (4) The law of the abutment pressure peak and the sphere of influence increase slightly, and the working resistance of support needed to be strengthened. (5) The subsidence quantity of the top coal in the control area increases along with the mining height in a quadratic polynomial way but decreases along with the initial supporting force in a negative logarithmic rule. (6) After assigning the subsidence, the regression relation between the initial supporting force and the mining height is a quadratic polynomial.
Highlights
Advances in Civil Engineering of the caving support is less than that of the large mining height support. e large mining height caving hydraulic support with a mining height of 5.2 m is under development, and the 7.2 m large mining height hydraulic support has been put into production. erefore, the support and supporting equipment for fully mechanized top coal caving with large mining height will be gradually improved [15,16,17]
E bottom coal cutting height is one of the key factors to determine whether the fully mechanized top coal caving can achieve high yield and high efficiency in the extrathick coal seam. e field is often estimated by experience, which often leads to poor results
It is worth mentioning that the flexible reinforcement of the prevention and control of large mining height coal wall spalling proposed by Zhang and Chen [23] and the step coal wall mining method proposed by Zhang et al [24] can fundamentally solve the problem of large mining height coal wall spalling
Summary
Article 68 of China’s “Safety Regulations for Coal Mines” clearly stipulates that caving top coal is strictly prohibited if the mining and caving rate is greater than 1 : 3. As for the current fully mechanized caving mining technology and equipment, the top coal caving thickness is three times thicker than the height of the bottom mining; a series of serious problems in overlying strata movement rule, mine strata behaviors and control, top coal recovery rate, and so on still exists which makes the application range of caving technology in coal seam thickness restricted seriously [1,2,3,4,5,6,7,8,9]. Based on the fact that the current bottom coal cutting height of fully mechanized top coal caving face in China is generally 2.0–3.0 m and some reach 3.8 m, the application of a coal seam with a thickness greater than 14 m thick is limited. Erefore, the support and supporting equipment for fully mechanized top coal caving with large mining height will be gradually improved [15,16,17]. E good relationship between support and surrounding rock is the key to give full play to the production capacity of large mining height fully mechanized caving mining. Is paper provides a reference for the selection of the coal cutting height of the bottom of the fully mechanized caving mining in the superthick coal seam. Considering the discontinuity caused by the appearance of joints, cracks, and so on, the mechanical properties of rock and coal measured in the laboratory are considered to have crack coefficients of 0.7 and 0.6, respectively. en the mechanical properties of each layer in the model were obtained by scaling the corresponding parameters of rock and coal measured in the laboratory based on similar theories
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