Abstract

Rockbursts, or coal bumps in coal mines, involve the spontaneous, violent fracture of rock. This paper discusses the application of energy concepts to back-analysis studies of coal bump events. Two-dimensional distinct element models were constructed of coal pillars with a range of material properties assigned to both coal material and rock-coal interfaces. These models were used to explore the compounding effects of the brittle failures of coal material and coal-rock interfaces on the energy release magnitudes. Loading conditions applied to these models represent a pillar failing individually as well as a full panel collapse. Results from the pillar models are presented in terms of the kinetic energy released from the unstable failures. Due to variation of coal and coal-rock interface properties, the magnitude of the excess kinetic energy was found to vary significantly. The total magnitude of kinetic energy released from the models was found to be significantly higher when brittle failure behavior was assigned to both the coal and to the coal-rock interface. This increase in excess energy indicated larger unstable failures and higher dynamic efficiencies under such material combination. In addition to the methodology for analyzing the effect of coal material and interface properties on the pillar failure stability, the paper also introduces and demonstrates a feasible failure mode for large widthheight ratio pillars.

1. INTRODUCTION

Compressive and shear slip failures emerge in deep underground mines under the influence of mining activities. Historically, several research efforts were made to address the role of excess energy on the initiation and occurrence of rockbursts, which included the Energy Release Rate (ERR) concept proposed by Cook [1] and Excess Shear Stress (ESS) presented by Ryder [2]. However, neither of these approaches accounts for brittle failure of rock and they have therefore not been ordinarily applied to study rockburst or coal bump incidents. In this paper, the commercially available software Universal Distinct Element Code (UDEC) is used to numerically model the failure instabilities and to present an illustration based on the unstable excess energy concept.

UDEC maintains the ability to simulate the quasi-brittle behavior of discontinuities through the Continuousyielding (CY) joint property [3, 4]. The Mohr-Coulomb strain-softening (MCSS) constitutive model may then be used to represent quasi-brittle material failure during unstable loading conditions [5]. The program also calculates the kinetic energy released and ultimately damped out during the simulation. A series of single pillar models were built with these combinations of tools to better understand the mechanism of bumps within wide coal pillars.

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