Numerical simulations of failure behavior around a circular opening in a non-persistently jointed rock mass under biaxial compression

Pre-existing discontinuities change the mechanical properties of rock masses, and further influence failure behavior around an underground opening. In present study, the failure behavior in both Inner and Outer zones around a circular opening in a non-persistently jointed rock mass under biaxial compression was investigated through numerical simulations. First, the micro parameters of the PFC3D model were carefully calibrated using the macro mechanical properties determined in physical experiments implemented on jointed rock models. Then, a parametrical study was undertaken of the effect of stress condition, joint dip angle and joint persistency. Under low initial stress, the confining stress improves the mechanical behavior of the surrounding rock masses; while under high initial stress, the surrounding rock mass failed immediately following excavation. At small dip angles the cracks around the circular opening developed generally outwards in a step-path failure pattern; whereas, at high dip angles the surrounding rock mass failed in an instantaneous intact rock failure pattern. Moreover, the stability of the rock mass around the circular opening deteriorated significantly with increasing joint persistency.