Uniaxial compression damage and crack propagation features of parallel double-fissure sandstones under high-humidity environments

Fractured pillars are eroded by gaseous water under high-humidity environments, and their hydro-chemical processes are closely related to the stability of the mineroom and ground subsidence. The uniaxial compression tests are carried out on standard sandstones with prefabricated parallel double-fissure to analyze the effects of high humidity on the strength-deformation properties, crack evolution and damage modes. By using the electron microscopy scanning and XRD diffraction, the microstructural changes and mass loss characteristics are analyzed before and after hydration. The results show that: (1) The higher humidity causes the structure to loosen more, the interlayer demarcation gets blurred, the number of microcracks grows and the rate of mass loss improves. (2) The damage modes contain tensile, shear and mixed tensile/shear damages. The crack growth includes in 4 types: wing cracks, tensile resistance cracks, and coplanar/non-coplanar secondary cracks. The crack propagation and damage modes are controlled by humidity. As the humidity increases, the crack initiation and penetration stresses drop, the number of cracks sprouting macroscopically reduces and the failure mode changes from shear to tensile failure. (3) The High-humidity condition produces water-rock chemical effects on fractured sandstones, weakening the structural surface of the cracks and the friction between the mineral particles, reducing the peak strength, peak strain and elastic modulus, increasing the Poisson's ratio and accelerating the destruction.