Analytical examination for the stability of a competent stratum and implications for longwall coal mining

Abstract

Rational estimation of the mechanical state of a competent rock layer is of prime importance for structural and support design in longwall coal mining. This paper analytically examines the stability of a voussoir-structured stiff rock by considering it acting as a symmetric flat arch with discontinuities at the abutments and midspan. Three typical failure modes including snap through, midspan crush and sliding failure are inspected. The solution assumes that the shape of the compressive arch obeys a parabolic variation as the voussoir beam deflects downwards with large-deformation. The crush failure due to stress concentration in the beam hinge is predicted by relating the squeezing area with the beam rotation, which is absent in previous studies. The proposed approach can examine the voussoir beam stability without cumbersome iteration. Primarily, this work facilitates the evaluation of the support requirements to reinforce roof beds in longwall panels. After accounting for the total loads of the overlying rock layers, the stability assessment developed in this paper can further be utilized to predict the span limit of the main roof above a longwall panel and to estimate the critical width which governs the magnitude of mining subsidence.