Microstructural deterioration mechanism and failure mode of water-immersed sandstone under uniaxial compression in Dazu rock carvings

Abstract

Understanding the microstructural deterioration and failure modes of water-immersed sandstone under load is crucial for comprehending the mechanical properties of grotto rock masses. This study conducted uniaxial compression tests on grotto sandstone samples with varying water contents, collecting acoustic emission (AE) signals during loading. Then, nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and computed tomography (CT) were employed to investigate the microstructural deterioration mechanism and failure mode of grotto sandstone. The results show that (1) The T₂ spectrum area and sandstone mass show similar exponential changes with the increase in water absorption time. During the unsaturated stage, the orderly diffusion and transfer of water result in the water component ratio reaching a dynamic temporary equilibrium stage, accompanied by significant deterioration. The deterioration of mechanical strength is mainly due to the formation of a large number of scaly attachments by illite when contacting bound water, which reduces the cementation strength between the particles. (2) The failure mode evolves from a combined shear-tensile failure to shear failure after water absorption. This transformation is accompanied by a decrease in crack porosity and fractal dimensions, indicating reduced complexity and volume of cracks due to water-weakening effects. (3) The dynamic evolution of multifractal parameters Δα and Δf based on peak AE frequency shows a decrease in Δα amplitude after the stable crack propagation stage, with AE signals becoming more uniform and shear dominated events becoming prominent. The research results provide reference value for the protection and restoration of grotto rock masses.