Temporal and spatial evolution of failure and fracture mechanisms in granite with en echelon joints

Abstract

En echelon joints within rocky slopes are highly susceptible to external forces, posing significant threats to slope stability and safety. The dip angles of such joints greatly influence the mechanical properties and failure characteristics of the rock mass. In this study, uniaxial compression tests were performed on granite specimens featuring joints with varying dip angles. The process of damage evolution was monitored using acoustic emission (AE) and digital image correlation (DIC) techniques. The following results were derived: All the tested granitic specimens with varying joint configurations exhibited a combination of tensile and shear failures, with tensile fractures accounting for more than 85% of the total fractures. DIC analysis revealed that stress was highly concentrated at the joints, with cracks initiating at the joint tips and propagating along the joint direction until the sample experienced brittle failure. Furthermore, the dip angle of the joints substantially influenced both the peak stress and cumulative AE counts of the samples. In particular, as the dip angle increased from 30° to 60°, the peak stress of the two-joint granite specimens increased by 22.8%, while their cumulative AE counts increased by 45.6%. Meanwhile, for the three-joint granite specimens, the peak stress increased by 37.0%, while the cumulative AE counts increased by 109.7%. Mathematical modeling revealed that peak stress increased exponentially with joint dip angle, while cumulative AE counts rose linearly. The research results enhance the understanding of the failure evolution of en echelon joints in rock mass.