In longwall top coal caving (LTCC), the resource recovery ratio of the working face is directly determined by the top coal recovery ratio. An investigation of the evolution of top coal drawing characteristics and revealing the evolution of top coal drawing parameters is necessary when providing guidance for caving parameter selection and improving the top coal recovery ratio. Based on in-situ measurements of the size distribution of caved top coal blocks in Wangjialing coal mine, a finite difference method (FDM)–discrete element method (DEM) coupled method was applied to establish a “continuous–discontinuous” numerical model and the process from the first coal drawing to the common coal drawing was simulated with 17 separate working face advances. The evolution of the drawing body (DB), loose body (LB), and top coal boundary (TCB) was obtained. The results show that, the evolution of parameters of DB such as shape and size, drawing amount, length and deflection angle of the long axis of the profile ellipsoid tended to decrease first, then increase, decrease again, and finally stabilise; the increment of the LB advance coal wall distance and the coal pillar distance was close to 0 m in the common coal drawing stage, while width increment of the LB was close to the drawing interval (0.865 m). The TCB formed after each coal drawing round was fitted based on the improved “Hook” function. The evolution of height and radius of curvature of TCB’s stagnation point was analysed. This was divided into three stages: the first (first to third drawing rounds) was the initial mining influence stage, the second (fourth to ninth drawing rounds) was the transitional caving stage, and the third (after tenth drawing round) was the common coal drawing stage.

In fully mechanized top-coal caving (FMTC), the effects of coal caving are closely related to the degree of damage to the top-coal which is determined by the stress state therein. Therefore, research into the evolution of mining-induced stress field is key to understanding failure mechanisms of top-coal. By taking the 12 309 FMTC face in Wangjialing Coal Mine (China) as the engineering background and using field measurement and numerical simulation, we studied the evolution of the principal stress field in FMTC under high horizontal stress. The research results demonstrated that in situ stress in Wangjialing Coal Mine was a high horizontal stress and lateral pressure coefficients in the north-south and east-west directions were 1.52 and 0.45, respectively. Under the influence of mining, principal stresses were concentrated in front of the coal wall, with concentration factors of 2.26, 2.24, and 2.85, respectively. The minimum principal stress in unconstrained sides of the top-coal in the roof-control zone was tensile. The directions of intermediate and minimum principal stresses in the top-coal were more sensitive to the influence of mining compared to the maximum principal stress. During rotation of the principal stress direction in topcoal, the location (19 m in front of the coal wall) where the maximum and intermediate principal stresses were equal and the location of the coal wall are key positions.

It is widely known that the triangle is the finest geometric unit, and therefore applying the triangulation joint to the rock mass simulation can not only accurately describe the fracture morphology of rock engineering, but also inversely deduce the mechanical parameters of blocks and joints. Based on the rock and soil two-dimensional analysis program (RS2), this paper compiles a program with MATLAB and realizes the parameterized setting of triangulation joint network (TJN) in RS2 for the first time, using it for the uniaxial compression model and roadway model accordingly. In the simulation of a RS2-TJN uniaxial compression model, its element parameters and joint parameters are calibrated according to the uniaxial compression strength and the elastic modulus obtained from the uniaxial compression test in a laboratory. Then its simulation results are compared with those of the particle flow code (PFC), which shows that the stress–strain curve obtained from the RS2-TJN uniaxial compression model matches the laboratory test one more closely. In the RS2-TJN roadway model, the simulation results obtained by adjusting the joint density are in good agreement with the roadway deformation in situ so as to study the failure characteristics of roadway surrounding rocks. Since the research on adding the triangulation joint network (cracks) to RS2 has not been found, its development and the realization of the parameterized control in this paper enrich the joint base of RS2 and provide a reference for the variety of joint numerical model.

The stable loading and operation of a coal bunker is critical for efficient production. In this study, the coal particle contact parameters were calibrated based on the angle of repose characteristics. The loading and discharging process of the coal bunker was simulated using the EDEM program. In addition, the flow pattern of the coal particles and the distribution characteristics of the wall pressure were investigated. The results indicate that the coal particles in the bunker can be divided into two flow patterns: mass flow and funnel flow. During discharging, the wall pressure fluctuated and exhibited a local over-pressure phenomenon, with a maximum pressure coefficient of 1.75. Finally, this study provides a reasonable explanation for the transformation of the flow pattern of coal particles and the distribution characteristics of wall pressure based on the mechanism of pressure arch influence. The findings of this study can provide theoretical guidance for designing coal bunker structures.