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Traditionally, longwall top coal caving (LTCC) panels adopt the single‐window drawing mode and their drawing efficiency is relatively low. The synchronous multi‐window drawing (SMWD) mode is a remarkable approach to resolve the incompatibility between shearer coal mining and top‐coal drawing. The present paper analyzes the caving characteristics of top coal under SMWD in LTCC mining of extra‐thick coal seam. The caving and migration of top‐coal fragments were simulated by using the continuum–discontinuum element method (CDEM). The results show that the SMWD mode can effectively improve the drawing smoothness with larger caving channels compared to the traditional single‐window drawing mode. The main caving channel for top‐coal fragments was directly above the assembled multi‐window (AMW), and the size of the AMW had a great influence on the distribution of the velocity field. Additionally, the simulated draw body of the initial drawing adopted an elliptical shape, which changed into a variation ellipse with the increasing size of the AMW. The boundary of the simulated draw body of the initial drawing presented an irregular shape that deviated from the results predicted by the Bergmark–Roos model. Furthermore, the drawing efficiency increased with the expansion of the AMW, whereas the recovery ratio first increased and then decreased with the expansion of the AMW. Finally, field tests revealed that the SMWD mode can greatly improve the drawing efficiency. Thus, the recovery ratio under A2 and A3 SMWD modes was higher than that of the traditional single‐window drawing mode. Based on the results of field tests and CDEM simulation, it is recommended to adopt A2 and A3 SMWD modes to enhance the top‐coal recovery ratio and drawing efficiency. These research results could constitute a technical reference for automated highly efficient top‐coal drawing and high‐yield LTCC panel extracting extra‐thick coal seam. [ABSTRACT FROM AUTHOR]

The dynamic sedation of the coal mine production is alternate or superimposed in coal rocks, which causes crack unevenness due to the presence of jacquards, causing unregistered coal blocks. By observing the deformation and fracture characteristics of coal-rock interbedding specimens with different gangue ratio under different stress paths, this paper studies the fracture instability mechanism and fracture characteristics of coal-rock interbedding, analyzes the progressive failure process and fracture opening model of coal-rock interbedding, and uses GDEM software to simulate the triaxial loading and unloading failure characteristics of coal-rock samples. The results show that the ratio of gangue inclusion has a significant effect on the structural strength of coal rock interbedding; with the unloading, the coal rock interbedding of the top coal body will be damaged and destroyed to varying degrees and asynchronously, the coal rock interbedding of the top coal body will present various forms of failure characteristics according to the changes of horizontal stress gradient in the vertical direction; the progressive failure process of coal rock interbedding under loading and unloading conditions can be divided into three stages. As the jigs are raised, the crack nonstable expansion stress of the composite coal body sample is gradually increased; and the rising ratio of the jacket X is not complete. The striped conjugated shear failure characteristics are more obvious; the different combined coal gangue tester shows microcrack near the peripheral loading boundary, and as the loading axis pressure increases, the fracture distribution range and density are increased; the rock layer is present. The tensile fracture is destroyed, and the coal seam exhibits shear destruction of intensive cracks; different test pieces produce significant tensile destruction on one side of the unloaded boundary; the greater the loaded axial pressure of the specimen, the greater the damage degree of the specimen after unloading; the damage degree of two coal and one rock specimens is the largest, the damage degree of one coal and one rock specimens is in the middle, and the damage degree of one coal and two rock specimens is the smallest. [ABSTRACT FROM AUTHOR]

The advanced deep hole blasting (ADHB) is commonly used to improve the fragmentation of thick hard top coal in longwall top coal caving (LTCC) mining. This paper presents an acoustic method to quantitatively evaluate the effectiveness of the ADHB. First, the variations of P‐wave velocity of hard coal samples under uniaxial and triaxial compression are obtained from the laboratory acoustic test. Then, an acoustic wave method based on seismic tomography is proposed to assess the effectiveness of the ADHB by introducing the P‐wave velocity attenuation model into the data processing. Finally, a field seismic tomography test is conducted to obtain the distribution of the P‐wave velocity of top coal before and after the ADHB implementation. And the P‐wave velocity attenuation is calculated to estimate the fragmentation effectiveness of ADHB. The results indicate that the P‐wave velocity attenuation model could well represent the broken degree of hard coal, suggesting that the proposed acoustic wave method could quantitatively evaluate the fragmentation effectiveness by exporting the nephogram of P‐wave velocity attenuation. The present study may provide technical support for improving the recovery ratio of thick hard top coal for LTCC mining. [ABSTRACT FROM AUTHOR]