Cyclic shear behavior of en-echelon joints under constant normal load

Abstract

En-echelon joints occur widely in rock masses and are often subjected to dynamic loads during earthquakes and rock bursts, which considerably influence stability in rock engineering. However, little is known of the cyclic shear behavior of en-echelon joints. This study conducted a series of cyclic shear tests on en-echelon joints under constant normal load (CNL) boundary conditions to investigate the cyclic shear behavior and dilation characteristics. The results show that shearing mechanisms of en-echelon joints were determined by joint angles during cyclic shearing, leading to differences in the evolution of shear resistance and dilation characteristics. A new phenomenon was observed, in that, shear stresses increased and decreased with an increase in the number of cycles during small and large shear displacements, respectively. The shear strengths and average dilation angles under cyclic shear loads decreased with increasing number of cycles. The difference in the peak shear stresses between en-echelon joints with different joint angles decreased with the number of cycles (N). Finally, dilation only occurred in the first several cycles, contraction predominated after several cycles, and the contraction of the specimens at a positive angle was larger than that at a negative angle. These findings hold crucial implications for predicting surface ruptures after earthquakes.