NONLINEAR FAULT BEHAVIOR NEAR UNDERGROUND EXCAVATIONS - A BOUNDARY-ELEMENT APPROACH

A boundary element model for stress/stability analysis of underground excavations in the vicinity of faults is presented. The boundary eleme nt formulation adopts the fictitious stress method for the simulation of excavation boundaries and the displacement discontinuity method for the representation of faults. The numerical model employs the Barton- Bandis non-linear joint model for the modelling of the fault behaviour and linear elastic behaviour for the rock. An incremental-iterative i n situ stress relaxation algorithm is implemented for the non-linear a nalysis of the faults. Both deformation and peak strength models of Ba rton-Bandis are incorporated for modelling the mechanical behaviour of the fault. The non-linear deformation of fault considers the effects of coupling between shear and normal stresses and displacement, joint closure, joint separation, hardening followed by post-peak or residual behaviour. The peak strength model employs a mobilized non-linear she ar strength envelope. The differences between linear and nonlinear sim ulation of the fault models are discussed. A comparison of model predi ctions with the classical Mohr-Coulomb peak strength model with consta nt joint stiffness is presented. The numerical model is used for a cas e study of Canadian hard rock underground mine. The shear and normal d isplacements along the fault during four mining sequences with backfil l simulation are presented and discussed.