The damage and deterioration effects of dry–wet cycles on impurity-bearing gypsum rock and a fractal damage constitutive model

Abstract

Uniaxial compression tests and scanning electron microscopy were utilized to investigate the mechanical deterioration and microstructural damage patterns of impurity-bearing gypsum samples affected by dry–wet cycles. The results show that as the number of cycles increases, the failure of axially compressed samples shifts from tensile-dominant to shear-dominant, and the uniaxial compressive strength (UCS) and elastic modulus decrease exponentially. Energy dissipation in loaded rock undergoes three stages of evolution prior to peak stress. The third evolution stage of samples subjected to cyclic processing appears to be prolonged relative to that of natural samples, suggesting that the brittleness attenuation of rock is caused by dry–wet cycles. Moreover, cycling-induced microstructural damage can be quantitatively characterized by the fractal dimension of defects, and the strong dependence of mechanical deterioration on microstructural damage was therefore elucidated in explicit functional forms. Additionally, a damage constitutive model with a microstructural damage variable was constructed. The responses of the UCS, strain, and brittleness of rock to dry–wet cycles are well characterized by the parameters of the model.