CDEM simulation of top‐coal caving characteristics under synchronous multiwindow drawing in longwall top‐coal caving mining of extra‐thick coal seam

Abstract

AbstractTraditionally, 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.