The uniaxial and conventional triaxial compression tests were conducted on granite from Sanjiang region of Yunnan-Tibet railway in the laboratory. The deformation characteristics and the damage evolution law of rocks were examined under different confining pressures. The results show that the internal cracks experience five stages during the compression deformation process, including no crack, crack initiation and stable propagation, crack accelerating propagation, crack decelerating propagation and crack termination. In addition, confining pressure significantly influences deformation characteristics of rock. Based on the above analysis and the damage model of micro units, a damage constitutive model is developed under the triaxial compression condition. The proposed model has a simple function form and distinct physical meaning parameters, which can be used to describe both the pre-peak and post-peak deformation characteristics of rocks. Furthermore, theoretical results obtained by this model are in good agreement with experimental results in the literature. The rationality of the model is verified by the parameter analysis.
Rock as a special geological material, after a long and complex diagenetic process, which contains a certain amount, different shape, the random distribution of micro porosity, crack, and presents the heterogeneity and anisotropy, etc. characteristics. The deformation behavior has obvious nonlinear characteristics. A disturbance in deep rock by the "three-high-one-destabilization" (high ground stress, high temperature, high karst water pressure and mining disturbance), induces many nonlinear engineering problems, such as brittle-ductile transition, rock burst and gas outburst. Therefore, it is of great significance to study the nonlinear deformation characteristics of rock and its damage evolution law.
A large number of triaxial tests for marble, granite, quartzite, sandstone, sandstone, shale had been done, which shows that the confining pressure is one of the important factors effecting rock deformation characteristics. Rock elastic modulus, yield stress, peak strength, residual strength and the peak strain have been increased as the confining pressure increase, and the confining pressure also plays a decisive role on failure model of rock. And a lot of theoretical research is carried out on the damage evolution law and the constitutive model of rock. A.L. Gurson has established a microscopic constitutive model from the perspective of the influence of micropore damage on material deformation behavior. M. k. Darabi et al. studied the phenomenon of damage recovery, and put the detailed damage constitutive model. Based on the analysis method of brittle or quasi-brittle solid materials based on damage mechanics, the damage constitutive model of DMG is proposed. Those researches modeled the deformation characteristics of rock stress-strain process pretty well, while there is few study focus on the post-peak deformation characteristics, especially the complete stress-strain relations including pre-peak and post-peak as a whole to study.
