Abstract:

Systematic experimental studies of granite from Dagangshan Hydropower Station were made and a series of stress-strain curves under different confining pressures were obtained. According to the active state of the microcracks existing in rock samples during the process in which the samples are loaded, four stress thresholds are defined, i.e. closure stress, initiation stress, damage stress and peak stress. These stress thresholds can represent the progressive damage process of granites and reflect the damage extent of rock samples. The pre-peak stress-strain curves can be divided into four stages in terms of character stresses. Deformation modulus and Poisson’s ratio should be calculated for each stage. It should be noted that the deformation modulus is not only related to the confining pressure but also to extent of damage of granites; and the Poisson’s ratio is only related to the rock’s extent of damage. Stress thresholds can be identified by volume strain-axial strain curve and linear regression technique. A constitutive model for granites in consideration of progressive damage is advised. In this model, the deformation parameters (deformation modulus and Poisson’s ratio) is regarded as function of stress and the strength parameters(cohesion and internal friction angle) is function of plastic strain. The model is embedded into general finite element software ABAQUS and a series of triaxial compression tests with different confining pressures are simulated. The results show that the simulated curves are close to the experimental curves; and the model can represent the nonlinear mechanical behavior of granite before its peak strength is reached.

Key words: progressive damage, character stress, constitutive model, numerical simulation with ABAQUS