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

• Underground engineering instability is associated with rock damage evolution. • The progressive fracturing in intact and jointed marble is studied. • The irreversible strains and dissipated energy are computed as damage variables. • The influence of the intermediate principle stress and joint are quantified. 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 (σ 1 > σ 2 > σ 3) 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 σ 1 and σ 3 directions change linearly with cumulative damage, whereas the irreversible strains in the σ 2 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 (σ 2 and σ 3), 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 σ 3 and a linear relationship with σ 2. 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. [ABSTRACT FROM AUTHOR]