Differential time-dependent fracturing and deformation characteristics of Jinping marble under true triaxial stress

Abstract

The conventional (σ1 > σ2 = σ3) multi-step creep test and true triaxial (σ1 > σ2 > σ3) multi-step creep test of Jinping marble with rectangular shape were conducted. In this way, the effects of σ1, σ2, σ3 and time on creep behaviour were compared and analysed. Unlike conventional creep tests, Jinping marble showed differential creep deformation and failure characteristics in σ2 and σ3-directions under true triaxial stress. The crack time-dependent evolution was-directional, and the crack tip growth was nearly parallel to the σ1-direction with high stress and opened along the σ2 and σ3-directions with low stress. Moreover, when σ2 > σ3, the crack growth in the σ2-direction was inhibited, and the crack evolution mainly occurred along the σ3-direction. This difference eventually led to the macroscopic failure plane of Jinping marble generally acting parallel to the σ2-direction and along the σ3-direction. The larger the value of σ2, the steeper the macroscopic failure surface, and the failure mode of the rock samples changed from shear to near-splitting failure: however, increasing σ2 can only cause closure of initial cracks opening along the σ2-direction, but did not change the number of initial cracks opening along the σ3-direction. The experimental data also showed that the differential creep deformation in the σ2 and σ3-directions caused by true triaxial stress did not change with time and σ1, but was only affected by σ2 and σ3. The differential creep deformation in σ2 and σ3-directions can be described by the formula DI = a(1-exp(b((σ2-σ3)/σ3))).