STRESS PATH AND PRECURSORS OF RUPTURE

In this paper, the conditions of rupture and rapture precursors of rock samples under different stress paths have been studied. We have done some experiments by three stress paths: (1) starting from a given stress state, we increased the maximum principal stress σ₁ and kept σ₂ and σ₃ constant until the rock sample failed (type A); (2) decreased the minimum principal stress until the rock sample failed (type B); (3) increased the minimum principal stress and kept the rock sample intact (type C). Experiments on samples of Jinan gabbro and Changping granite allow us to compare the rupture strengths for the A and B type of stress paths. Besides, we also compared the volumetric strains, acoustic emission, and velocity V_p for all three types of stress paths.For the A type, rupture precursors conform with the results of previous studies by other authors. In case B, the rock samples were in a super-dense state before rupture the related increase of acoustic emission and reduction of velocity V_p however appeared very late. In case C, the rock samples were in an over-dilatant state, increase of aeoustic emission and dropping of velocity V_p, appeared but no rupture occurred.