Numerical Study on Effect of Joint Strength Mobilization on Behavior of Rock Masses with Large Nonpersistent Joints under Uniaxial Compression

In this paper, by analyzing evolution of aperture and contact forces of joints as well as parallel bond breakage, the effect of joint strength mobilization on mechanical behavior of jointed rock masses was studied numerically through particle flow modeling package PFC2D. With the calibrated microparameters of the particles, parallel bond contacts, and the smooth-joint contacts, the numerical tests reproduced the dependence of strength reduction and multipeak deformation behaviors of the specimens with large nonpersistent open joints on joint orientation and spacing that was observed in the laboratory tests. Four types of stress-strain curves [i.e., the single-peak curve (Type I) and the three multipeak curves (Types II-IV)] were related to the different closing and strength mobilization processes of the joint system. Strength immobilization of the joint system with the opening of most joints and slight strength mobilization of the joint system with partial closing of some joints after peak strength led to Type I (strain softening) and Type II (general strain softening with oscillations) behaviors, respectively. Full strength mobilization of the joint system with entire closing of all joints accompanied by severe damage developing in the matrix at the first peak (peak strength) led to Type III (yield platform-strain softening) behavior. Salient strength mobilization of the joint system with entire closing of most joints at the last peak (peak strength) as well as damage in the matrix mainly developing after the first peak led to Type IV (yield platform-strain hardening-strain softening) behavior. Salient or full strength mobilization of the joint system for the specimens with small joint inclination angles, or little interruption in axial load transferring for the specimens with large joint inclination angles induced slight or moderate strength reduction, whereas both slight strength mobilization of the joint system and strong interruption in axial load transferring for the specimens with medium joint inclination angles induced sharp strength reduction.