Interaction of two offset parallel flaws in geomaterials under unloading conditions

Abstract

Rock excavation operations (also known as unloading) in high rock slopes, tunnels, and underground engineering cause large and extensive stress relaxation, even accompanied by the generation of tensile stress. Nevertheless, there have been few studies on the theoretical damage mechanism of rock under unloading conditions. In the present work, based on the superposition principle and the classic Kachanov method, we first proposed a theoretical calculation method for the stress intensity factor (SIF) at the tips of two parallel-offset flaws under unloading conditions. Then, a theoretical analysis of the effect of various geometric factors, such as flaw staggered distance, rock bridge length, flaw length and inclination angle, was carried out. The interaction between two offset flaws was captured. The results support the following findings: 1) The smaller the staggered distance or the rock bridge length is, the larger the flaw length, and the interaction between the two flaws becomes more significant. 2) With increasing inclination angle, the tendency of tensile failure becomes more obvious, while that of shear failure weakens. 3) The longer the rock bridge length, the more significantly the flaw interaction is affected by the inclination angle. Finally, discrete element simulations were carried out to verify the theoretical analysis results, and good consistency was found. These research results are helpful for understanding the failure mechanism of fractured rock masses caused by excavation (unloading condition).