The Impact of Abutment Relaxation on Stability of Underground Mine Openings

ABSTRACT: In contrast to typical excavations in civil engineering construction, mine openings often create locally reduced confinement and relaxation or tension in the backs or walls. Boundary-parallel stress reduction, or relaxation, can have devastating consequences in structurally dominant ground or in situations where the ground has been previously damaged by high stress. Such relaxation is often neglected in limit equilibrium calculations and in empirical design techniques. The stability of hanging walls in open stopes is of particular concern with respect to the detrimental impact of relaxation on both rockmass stability and the capacity of standard cablebolt reinforcement systems. The voussoir analogue for jointed beam stability is used to investigate the impact of stress reduction parallel to the back and walls of underground mine stopes and to provide an relaxation adjustment factor for the empirical "Stability Graph", a technique for design of open stope dimensions and support.