Intermediate Principal Stress Effects on the 3D Cracking Behavior of Flawed Rocks Under True Triaxial Compression

Abstract

Abstract Crack initiation, growth, and coalescence in flawed rocks have been extensively studied for 2D (planar, penetrating) flaws under uniaxial/biaxial compression. However, little is known as to the mechanisms and processes of cracking from 3D flaws under true triaxial compression, where the intermediate principal stress ($$\sigma _2$$ σ 2 ) is distinguished from the major and minor principal stresses. In this work, we systematically investigate the effects of $$\sigma _2$$ σ 2 on the 3D cracking behavior of rock specimens with preexisting flaws, through the use of mechanistic simulations of mixed-mode fracture in rocks. We explore how two characteristics of $$\sigma _2$$ σ 2 , namely, (i) its orientation with respect to the flaw and (ii) its magnitude, affect two aspects of the cracking behavior, namely, (i) the cracking pattern and (ii) the peak stress. Results show that the orientation of $$\sigma _2$$ σ 2 exerts more control over the cracking pattern than the flaw inclination angle. The peak stress becomes highest when $$\sigma _1$$ σ 1 is parallel to the flaw, whereas it becomes lowest when $$\sigma _2$$ σ 2 is parallel to the flaw. Also, the effects of $$\sigma _2$$ σ 2 magnitude are more significant when $$\sigma _2$$ σ 2 becomes more oblique to the flaw plane. On the basis of our observations, we propose mechanisms underlying the cracking behavior of 3D flawed rocks under true triaxial compression. Highlights The effects of the intermediate principal stress ($$\sigma _2$$ σ 2 ) on the 3D cracking behavior of flawed rocks under true triaxial compression are systematically investigated. The orientation of $$\sigma _2$$ σ 2 exerts more control over the cracking pattern than the flaw inclination angle. The effects of $$\sigma _2$$ σ 2 magnitude become more significant when $$\sigma _2$$ σ 2 are more oblique to the flaw plane. Mechanisms underlying the cracking behavior of 3D flawed rocks under true triaxial compression are proposed based on the observations made.