Research on the required width of a fault waterproof coal pillar based on underground pressure control theory

Abstract

Based on underground pressure control theory, this paper expounds the distribution characteristics of abutment stress and the resulting damage to a coal seam in front of a working face. In addition, the distribution and propagation features of vertical underground pressure in floor strata is characterized by simulation results obtained from 2D-σ finite element analysis software. Numerical simulation reveals that the peak stress line of the vertical underground pressure is inclined toward the coal mining direction of the working face. Based on the establishment of a mechanics model for water inrush from floor aquifer through a fault in a stope, a formula for calculating the distance between the bottom of the coal seam and the intersection point of the peak stress line with the fault is derived. The condition allowing water inrush from a floor aquifer through a fault is described as follows: the destroyed floor depth caused by underground pressure is not less than the distance between the bottom of the coal seam and the intersection point of the peak stress line with the fault. The water inrush pathway is composed of the fault and the floor strata destroyed by underground pressure. Based on gray multivariate nonlinear regression analysis, the formula for calculating the destroyed floor depth with four main factors is deduced: these factors are the mining depth, dip angle of the coal seam, inclination width of the working face, and Platts’ coefficient of the floor strata. According to the mechanics model for water inrush from a floor, the formula for a fault waterproof coal pillar in a stope is presented, and the rationality of the model and formula has been verified by cases of water inrush from floor aquifers in the Suncun Coal Mine and the Xiaoyun Coal Mine, China.