Influence of intermediate principal stress on failure mechanism of hard rock with a pre-existing circular opening

ZHANG She-rong(张社荣)¹, SUN Bo(孙博)^{1, 2}, WANG Chao(王超)¹, YAN Lei(严磊)^{3, 4}

(1. State Key Laboratory of Hydraulic Engineering Simulation and Safety (Tianjin University),
Tianjin 300072, China;
2. China Water Resources Beifang Investigation, Design and Research Co. Ltd, Tianjin 300222, China;
3. School of Civil Engineering, Tsinghua University, Beijing 100084, China;
4. Hydropower Kunming Engineering Corporation, Kunming 650051, China)

Abstract:Based on particle flow theory, the influences of the magnitude and direction of the intermediate principal stress on failure mechanism of hard rock with a pre-existing circular opening were studied by carrying out true triaxial tests on siltstone specimen. It is shown that peak strength of siltstone specimen increases firstly and subsequently decreases with the increase of the intermediate principal stress. And its turning point is related to the minimum principal stress and the direction of the intermediate principal stress. Failure characteristic (brittleness or ductility) of siltstone is determined by the minimum principal stress and the difference between the intermediate and minimum principal stress. The intermediate principal stress has a significant effect on the types and distributions of microcracks. The failure modes of the specimen are determined by the magnitude and direction of the intermediate principal stress, and related to weakening effect of the opening and inhibition effect of confining pressure in essence: when weakening effect of the opening is greater than inhibition effect of confining pressure, the failure surface is parallel to the x axis (such as σ₂=σ₃=0 MPa); conversely, the failure surface is parallel to the z axis (such as σ₂=20 MPa, σ₃=0 MPa).

Key words:rock mechanics; intermediate principal stress; hard rock with pre-existing circular opening; failure mechanism; discrete element