Evolution characteristics of the irreversible strains and mechanical parameters of Jinping marble were investigated using the combination of uniaxial and triaxial compression tests as well as triaxial cyclic loading and unloading tests. Compared with the results of stress-strain curves, strength and failure modes under different conditions, it was found that the testing results were valid under cyclic loading and unloading tests. The experimental results also demonstrated that with the increase of the rock damage, the lateral irreversible deformation was always greater than the radial one but less than the volume one. The irreversible strains could be quantified by two damage stages, namely, the linear and the nonlinear rising stage. The linear increase of irreversible deformation was mainly caused by micro crack initiation and propagation, and the nonlinear increasing trend could be attributed to micro cracks through each other. The relationship between these irreversible strains and equivalent plastic shear strains was established. Moreover, the physical meanings of these fitting parameters were analyzed.
At present, with the increasing depth of mining, civil engineering and underground laboratory, excavation of deep tunnels always causes stress concentration, thus resulting in brittle fracturing of surrounding rock (Liu et al., 2016). This failure behavior is strongly influenced by the confined pressure (Qiu et al., 2010). Therefore, in order to study the engineering stability, it is meaningful to investigate the mechanical properties of hard rock.
In the last decades, a large number of researchers have studied the mechanical response of hard rock under uniaxial and triaxial loading tests. On one hand, some researchers focus on the rock damage evolution and irreversible strains characteristics using the damage-control tests. For instance, Martin and Chandler (1994) investigated damage stress of Lac du Bonnet granite and distinguished stress-strain curves based on the characteristics of crack development. Eberhardt et al. (1999) studied the failure process of granite using the normalized method. Qiu et al. (2014) paid attention to the irreversible strains in the pre-peak stage using cyclic loading and unloading tests of confined pressure. On the other hand, the variation of mechanical parameters from damage variables has also been studied by many researchers. For instance, Su and Yang (2006) summarized the deformation and strength characteristics of marble with different types of crystal particles. Zhang (2010) established the elastoplastic coupling model of marble. Zhao et al. (2010, 2014) discussed the dilatancy of rock under triaxial tests.
