Prediction of the height of caving and fracturing above an isolated longwall extraction panel

Abstract

The height of collapse above a longwall extraction panel is simulated assuming a transversely isotropic continuum and an isotropic strength criterion. The transversely isotropic assumption allows consideration of the role of overburden conditions, specifically the spacing of bedding discontinuities. The shape and height of the collapse zone are like those produced in physical models and are consistent with subsidence measurements. The interaction between the disruption and break-through to the surface is examined using voussoir beam analysis. Break-through to the surface, which implies a fracture connection to the extraction level, may be associated with surface subsidence in excess of about 300 mm or a compressive strain in excess of about 4 mm/m.