An aftermath analysis of caving characteristics and movement of overlying strata in fully mechanized longwall gob

Abstract

The large-scale collapse of overlying strata in the gob directly affect the safe production of coal mines; they are also the major causes of geological disasters, such as ground cracks, surface subsidence, and ground collapse. In this paper, the movement and caved characteristics of overlying strata during coal seam excavation are studied by conducting a physical model experiment. Results show that overlying strata have different movement and caved laws during the initial, intermediate, and later mining stages. During the initial mining stage, overlying strata do not collapse, and the subsidence is extremely small. During the intermediate mining stage, overlying strata cave along the vertical direction, and caved height gradually increases. Large numbers of cavities, abscission layers, and fractures exist between caved strata. The fractured area gradually increases upward, and the subsidence increases considerably. During the later mining stage, overlying strata cave along the horizontal direction. The abscission layers between the caved strata of the central are compacted. The compacted area is surrounded by a fractured area. The compacted and fractured areas increase along the horizontal direction. The subsidence curves exhibit a horizontal variation. Overlying strata evolve from the self-equilibrium stage to the vertical collapse stage, and finally, the horizontal collapse stage. The fractured area changes from a no fractured area to a fractured area, increases vertically, and finally, increases horizontally. The subsidence curve changes from extremely small to large, and finally, changes horizontally. Keywodrs Longwall mining, Gob, Overlying strata, Movement, CavedLongwall mining is widely used in underground coal mining 1-3 . This automatic mining method exhibits the advantages of large coal production and high efficiency 4-6 . In China, about 95% of underground coal mines use the longwall mining method, which provides technical guarantee to the development of China's coal resources 7 . The coal production of China has become the largest in the world 8,9 . Coal accounted for 55.3% of China's total energy consumption in 2023. At present, coal is still the main energy source in China.After coal is extracted from the underground, the original equilibrium state of the strata is changed 10-14 . The stress is redistributed, and overlying strata of coal seam are deformed and destroyed [15][16][17][18] . Overlying strata are affected by coal seam mining in different degrees, leading to varying levels of deformation and failure [19][20][21] . The caved, fractured, and continuous deformation zones are formed from bottom to top [22][23][24] . When a sufficiently wide longwall panel is mined, overlying strata can form the caved, fractured, continuous deformation, and soil zones 25 .The caved zone is dominated by broken rock, without continuity and bedding plane. A large number of voids and fractures exist between caved strata 26,27 . The fractured zone is at the upper part of the caved zone. The caved strata of the frac...