On the excavation-induced stress drop in damaged coal considering a coupled yield and failure criterion

Abstract

Investigating the stress drop of abutment pressure is the key to a deep quantitative analysis of the discontinuous stress redistribution under mining. In the present study, uniaxial and triaxial compression tests are carried out separately to determine the bulk and shear moduli, the cohesion, and the internal friction angle of the coal samples. By extending the meaning of Mohr’s circle referring to yield stress instead of the maximum principal stress, a yield line is introduced to illustrate the stress drop of Mohr’s circle referring to yield stress instead of the maximum principal stress at the elastoplastic boundary. Furthermore, a theoretical solution of the stress drop as a function of the damage is proposed to investigate how the abutment pressure differs considering the yield line and failure line. In addition, applying the stress drop at the yield line in non-pillar mining, top coal mining, and protective coal mining shows that the damage has a nonlinearly positive influence on the stress drop. The results shows that the bulk modulus and internal friction angle have a more sensitive influence on the stress drop than do the shear modulus and cohesion. Finally, the stress drop is divided into a discontinuous stress drop at the yield line and a structural stress drop at the failure line. The stress drop is effective in describing the discontinuous stress redistribution and shows a clear difference in the movement direction of Mohr’s circle considering the unloading pressure.