Experimental study on evolution of normal stiffness of granite joints treated by chemical corrosion

In this study, the variation characteristics of normal stress and normal closure of granite joints were studied. The effect of chemical solution with different pH values (1, 3, 7, 12), the corrosion time t (10, 30, 100 d) and various initial openings b on the evolution of the specific normal stiffness of the specimens were revealed through normal load compression tests taking into account constraint circumferential stiffness boundary conditions. The experimental results indicate that the normal stress-normal strain curves of specimens with mismatched joints are different from the intact specimens and specimens with matched joints. Due to the crushing of the asperity on the surface of the joints, the local stress drop phenomenon occurs during the overall growth process of the stress strain curves. The normal closing curve of mismatched joints exhibit nonlinear characteristics, in which the increasing rate of normal displacement first increases and then decreases with the increment of normal stress. Under the same normal stress, both the normal displacement and the closing rate increase with the increment of the initial opening. By introducing several classical joint closure models, it is found that the normal stress and stiffness of joints are affected by the initial opening, pH value and corrosion days, among which the initial opening is the most import. When pH = 1 and t = 10 d, with an increase of normal displacement from 1-3 mm, the normal stress of the specimens with b = 1.65 mm increase by 46.26 %-149.46 %, compared with the specimens with b = 3.4 mm. The specific normal stiffness of the mismatched joints decreases with the reduction of pH value. The normal stiffness of joints in different chemical solutions decreases first and increases then as the corrosion time increases.