Numerical Investigation of Top Coal Drawing Evolution in Longwall Top Coal Caving by the Coupled Finite Difference Method-Discrete Element Method

Abstract

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.

Research on Coal Gangue Recognition Based on Multi-source Time–Frequency Domain Feature Fusion

“…Fully mechanized top coal caving is one of the main mining methods suitable for thick and extra-thick coal seam mining in China, which has many advantages such as low cost, low tunneling rate, high recovery rate, and strong adaptability. , …”

“…Fully mechanized top coal caving is one of the main mining methods suitable for thick and extra-thick coal seam mining in China, which has many advantages such as low cost, low tunneling rate, high recovery rate, and strong adaptability. 33,34 The coal seam generally occurs in the coal-bearing rock formation, located between the roof and floor strata. With the advancement of coal mining at the working face, the coal seam floor plays a supporting role, and the roof is above the coal seam.…”

Drilling study of bit in gravel environment based on DEM–MBD

“…The auxiliary installation device for rock bolt drilling In the 20th century, Cundall et al [12][13][14] proposed the discrete element method (DEM), and simulated the conveying performance of screw conveyor for the first time through DEM. Nowadays, DEM has become the main application method for simulating screw conveying, and it is also widely used in geotechnical field, [15][16][17] mining field, [18][19][20] chemical field, [21][22][23] and agricultural field. [24][25][26] With the continuous improvement and development of the DEM, it has been widely used in the field of bit research to construct different drilling environments through DEM, and then analyze the particle movement in the drilling process.…”

Precise detection of coal and gangue based on natural γ-ray

“…Jingjing Deng et al employed terahertz technology to generate images of coal gangue mixture for the purpose of coal gangue detection 25 – 28 . Yuming Huo optimized the parameters of intelligent coal drawing process by establishing a predictive model of the periodic coal drawing time 29 , 30 .…”