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

The conventional (sigma(1) > sigma(2) = sigma(3)) multi-step creep test and true triaxial (sigma(1) > sigma(2) > sigma(3)) multi-step creep test of Jinping marble with rectangular shape were conducted. In this way, the effects of sigma(1), sigma(2), sigma(3) and time on creep behaviour were compared and analysed. Unlike conventional creep tests, Jinping marble showed differential creep deformation and failure characteristics in sigma(2) and sigma(3)-directions under true triaxial stress. The crack time-dependent evolution was-directional, and the crack tip growth was nearly parallel to the sigma(1)-direction with high stress and opened along the sigma(2) and sigma(3)-directions with low stress. Moreover, when sigma(2) > sigma(3), the crack growth in the sigma(2)-direction was inhibited, and the crack evolution mainly occurred along the sigma(3)-direction. This difference eventually led to the macroscopic failure plane of Jinping marble generally acting parallel to the sigma(2)-direction and along the sigma(3)-direction. The larger the value of sigma(2), the steeper the macroscopic failure surface, and the failure mode of the rock samples changed from shear to near-splitting failure: however, increasing sigma(2) can only cause closure of initial cracks opening along the sigma(2)-direction, but did not change the number of initial cracks opening along the sigma(3)-direction. The experimental data also showed that the differential creep deformation in the sigma(2) and sigma(3)-directions caused by true triaxial stress did not change with time and sigma(1), but was only affected by sigma(2) and sigma(3). The differential creep deformation in sigma(2) and sigma(3)-directions can be described by the formula DI = a(1-exp(b((sigma(2)-sigma(3))/sigma(3)))).

Automated summary

The study found that under true triaxial stress, Jinping marble exhibited directional crack evolution, with the macroscopic failure plane generally parallel to the σ2-direction and extending along the σ3-direction.