Development of a 3D Elasto-plastic Model for Simulation of Progressive Roof Caving in Underground Coal Mines

A reliable knowledge of caving behaviour of strata is one of the basic requirements for successful planning, design and safe extraction in underground coalmine workings. This papers describes a three–dimensional large strain elasto-plastic model implemented in combination with modified Mohr-Coulomb failure criteria for an improved and field representative simulation of failure and caving of overlying strata with progressive face advance. The modelling study has been done for a typical bord and pillar depillaring and a longwall working. The results show that the proposed model is capable of capturing the basic mechanism involved in shear and tensile failure and subsequent caving of strata with progressive advance of face. The load on support and face convergence plots adequately satisfy the basic understanding of typical strata behaviour in a longwall working. The results of three dimensional model provides a better insight of initiation of failure in various roof layers and their propagation with regard to the simulated mining cycles in the mine workings. It shows that a thicker roof layer undergoing shear failure plays the most dominant role in defining the overall caving behaviour of strata in deep mine workings. However, when the layers are relatively thinner, the dominant failure mechanism leading to caving of strata is tensile while shear failure occurs after softening of the layers predominantly along the edges and also along the line of extraction which significantly influences the induced stress in the strata ahead of the extraction line. The results obtained from this study have provided an improved understanding of the complex caving mechanism associated with underground coalmine workings.