Numerical observations of the failure of a laminated and jointed roof and the effective of different support schemes: a case study

Abstract

Roof failure related to laminated and jointed rock masses has been recognized as a major cause of fatalities in underground coal mines. This paper presents numerical simulations of the failure of a laminated and jointed roof using the discrete element method, while focusing on the initiation and propagation of (and the interactions between) microcracks and macroscopic fractures and the development of the associated damage, stress and deformation in the laminated and jointed roof. Numerical modeling shows that the behaviors of bedding planes and vertical joints governed the progressive failure of the laminated and jointed roof. Microseismic activity corresponding to the development of microcracks in the roof intensified before major roof displacements and subsided in the later stages; such activity could serve as a precursor of roof fall events. The effectiveness of various support elements (rock bolts, metal meshes, and anchor cables) on the roof stability was numerically evaluated. Rock bolts and/or anchor cables produced a banded compressive stress in the laminated roof, restricting the separation of bedding planes. Rock bridges in the bolted roof suppressed the formation of macroscopic fractures and significantly reduced the interactions between fractures. The roof skin support with a metal mesh provided confinement to the fractured roof, thereby preventing fragmented rocks from falling and restricting progressive spalling between bolts. The numerical simulations presented in this paper can be helpful for understanding the likely failure mechanisms of laminated and jointed roofs and for finding potential solutions.