Numerical Evaluation of Coal Pillars with Rock Partings or Bands

ABSTRACT: The design of underground coal pillars requires a reliable estimation of both pillar strength and pillar stress. ACPS, a empirical pillar design tool, utilizes the Mark-Bieniawski empirical pillar strength formula with pillar loads that are estimated using the tributary area method, load transfers from neighboring pillars as well as the distribution of abutment loads. Subsequently, the safety/stability factor is determined from these empirical tools. ACPS estimates the pillar strength using a 900 psi coal mass strength value. As the quality of coal reserves changes and rock inclusions increase, the behavior of the pillars can change. Numerical modeling tools based on the finite element method are utilized in pillar design to determine stress redistribution in the pillar and around the opening; however, these numerical methods cannot estimate the strength of the pillar. This paper presents numerical models of pillars with various geological inclusions. Numerical modeling will be used to analyze the effect of geological factors and horizontal stress ratios on pillar strength and stress distribution. A comparison of the stress distribution across the mid height of the pillar, RS2 strength factor, and the proportion of yielded mesh and interface elements is included.