Study on damage evolution of intact and jointed marble subjected to cyclic true triaxial loading

Abstract

Rock masses in underground engineering, such as mining and deep tunnelling engineering, are often repeatedly loaded and unloaded. Here, a series of true triaxial multi-level single cyclic loading tests (σ1 > σ2 > σ3) were carried out on intact and jointed marble (50 × 50 × 100 mm3) to investigate the influence of the stress state and the absence or presence of a joint on the progressive damage process. The test results show that rock damage is directional and anisotropic. The irreversible strains in the σ1 and σ3 directions change linearly with cumulative damage, whereas the irreversible strains in the σ2 direction decrease nonlinearly. The dissipated energy is appropriately linearly related to the equivalent irreversible strains. The damage variables based on the irreversible strains and dissipated energy are closely correlated, as determined by their similar fitted parameters. The stress state (σ2 and σ3), the absence or presence of a joint and the brittleness play a vital role in the rock damage evolution. More specifically, the parameter a has a logarithmic relationship with σ3 and a linear relationship with σ2. The relationship between the parameter a and the joint dip angle β can be fitted by a Gaussian distribution. In addition, the fitted parameter a decreases with increasing brittleness.