Numerical investigation of the effects of coal seam dip angle on coal wall stability

Abstract

Instability and failure mechanism of coal wall at coalface is one of the hot-button and difficult issues in the study of coal mine ground control. Research to date has mainly focused on the macro-characteristics of coal face failure whereas few efforts have been devoted to the micro aspects or to the mechanisms behind these failures. The work described here takes coal face 8102 in the Wolonghu Mine, China, as an example and employs distinct element numerical software (UDEC) to investigate the distribution of abutment stress in front of the coal face at different mining dip angles from micro and macro perspectives, and reveal the main failure form and location of coal rib. The numerical results indicate the following six points. (1) The distance between the location of the peak abutment stress and the coal face increases with greater mining dip angles. (2) The rank by angle of abutment stress concentration factors is horizontal >up-dip> down-dip coal faces.(3) Tensile fractures dominate the failure of horizontal and up-dip coal faces and the only difference between the two is the form of the failure. (4) Shear fractures are the dominant failure components of down-dip coal faces. (5) The coal face failure forms include integral rib spall and a combination of upper-rib shear failure and roof caving. (6) Tensile fractures are mainly responsible for roof failures. The difference in roof movement between up-dip and down-dip coal faces is reflected in the forms of failure of their coal faces and of their roofs. Moreover, the effect of coalface depth, mining height, panel advance velocity and coal strength on the stability of coal rib is studied. The conclusions obtained from numerical simulation are consistent with engineering result, which verifies the reasonability of simulation analysis by UDEC. Finally, we propose measures to avoid coal face failure in the Wolonghu mine considering the numerical outcomes, the monitored strata behavior, and the recorded setting support resistance.