The complete properties of rocks under uniaxial loading were studied on the basis of nonlinear theory and damage mechanics in this paper. According to the definition of damage strain of rocks, a damage strain method by which the damage variable was defined was suggested to establish the rheology damage constitutive model of rocks. And this model was verified via computer modeling of stochastic rock failure and analyzing the stability of slope.
Rheology is one of the most important properties of rocks that influence the stability of rock engineering. Many research results of rheology have been given, but most of them were just based on linear theories. So several problems haven't been solved.
Domino effect of loading rate on quantitative analysis of strength
Domino effect of loading rate on quantitative analysis of modulus.
No quantitative description of the rule between creep life and creep stress.
Recently, with the fast developing of nonlinear theories and damage mechanics, they were being applied in the studies of rock engineering. Kachanov first (1958)advanced the damage conception in 1958 while studying the creep rupture process of the metal. In 1976, Dragon and Mroz constituted a continuum damage model based on the concept of fracture area. In the sequel, many scientists such as Krajcinovic (1981), Kachanov(1982), Costin(1983), applied damage mechanics to study the damage properties of rocks from different view or points. At present, several representative damage theories were suggested and applied:
The conception of effective modulus was put forward to define the damage variable. Commonly, the unloading modulus was thought as the effective modulus of damage. But there are many disputed opinions on this conception.
The conception of effective areas was suggested to define the damage variable of rock masses. Fracture mechanics must be applied in this method.
Desai model. Desai thought that the rock could be divided into two parts: damaged and undamaged. The property of rock depended on the joint action of the two parts.
Micro-damage theory. In this theory, the influence of the distribution of micro-cracks was considered.
In recent years, Okubo and Jin have made systemic experiments to analyze the properties of rocks, including loading rate tests, creep tests, relaxation tests, unloading tests ere. Conclusions have been given:
The shape of complete stress-strain curves of rocks under tensile loading is similar to the shape of the curves under compression loading.
The law of loading rate dependence of the tension strength is similar to that of the compressive strength.
In tests, with the variation of stress fields, the failure patterns of rocks will change. In compression tests, the failure patterns are controlled by the confining pressure. At zero confining pressure, axial splitting occurs along a series of vertical surfaces. For low confining pressure, failure develops along a pair of conjugate shear planes.
