3D strain softening modelling of coal pillars in a deep longwall mine

Abstract

In longwall coal mines, the entries on both sides of the panel play a significant role in production rate and safety of operation. With increasing production amount, the rate of conveying material through such entries increases. Therefore, it is required to design wider entries. Support of these entries, particularly in deep mines is difficult. In this paper, by using FLAC3D program code a deep longwall coal mine is modeled. The coal seam has a strain softening property, and the analysis index of stress and deformation of ribsides and coal pillars at different loading levels are determined. Strain softening parameters is studied separately for each modeled coal pillar, and based on conventional formula the pillar strength are calculated. In a modeled longwall mine, the caving material at goaf zone are fully compact. The results shows that based on Mohr-Coulomb model, the strain softening occurs at maximum cohesion and friction, and at region of decreasing the strength of pillar in stress-strain curve. Because of 3D nature of analyses, the effect of front and side abutment load on stability of pillar are studied simultaneously. Therefore, the results of this study could be suitable criteria for appraisal of pillar design method at deep longwall coal mines.