ABSTRACT
The presence of discontinuities in strong rock masses creates blocky structures that give an overall different behaviour than an assumed continuous medium with adjusted mechanical properties if the non-jointed rockmass shear strength is higher than that of the rock joint. In this research, numerical simulation is used to investigate the effect of persistent and non-persistent discontinuities in the formation of plastic zone around a deep, circular tunnel. Parametric analyses for persistent joint sets are initially carried out investigating the effect of the presence of up to three joint sets, their spacing with respect to the excavation scale, and their strength parameters, i.e., joint friction angle and joint cohesion with respect to the initial stress field. Then, statistical analysis is used to deepen the understanding of the effects of joint length and spacing for non-persistent discontinuities, i.e., when rock bridges are formed around the excavation. The analyses results are used to identify the critical level of deconfinement in the development of plastic zone around the excavation.
