Damage Evolution and Constitutive Model of Sandstone Under Hydro-Mechanical Coupling

Abstract

To study the influence of water content on the deformation mechanical properties and damage evolution characteristics of sandstone, uniaxial compression tests were carried out on 5 kinds of sandstone with different water content using deep soft rock T-P coupling adsorption analysis system. Based on the attenuation characteristics of elastic modulus and considering the initial water rock action and subsequent load action, the total damage variable of sandstone under hydro-mechanical coupling was derived. A theoretical model that can simulate the whole damage evolution process was established by Logistic function, and a piecewise constitutive model was established combining damage mechanics and effective medium theory. The results show that: (1) With the increase of water content, the uniaxial compressive strength, elastic modulus and brittleness of sandstone decrease gradually, and the initial damage degree increases; (2) The theoretical damage evolution process established based on logistic function can be divided into four stages: initial damage retain, damage initiation, damage acceleration and damage deceleration termination, which can effectively simulate the whole damage process characterized by macro parameters; (3) The piecewise constitutive model can effectively simulate the whole stress-strain curve of sandstone under different water content, and the theoretical curve is in good agreement with the experimental data; (4) The parameters a and r in the constitutive model jointly determine the shape of theoretical constitutive relationship curve. Parameter a reflects the initial damage degree, while parameter r reflects the damage evolution rate. The increase of water content will lead to the initial damage of sandstone and inhibit the damage evolution rate. This paper has some theoretical reference value for understanding the damage evolution characteristics of sandstone under the hydro-mechanical coupling.

Keywords: Water content, Damage evolution, constitutive model, Initial compaction, Hydro-mechanical coupling