Fracture characteristics and failure analysis of underground caverns in Longyou Grottoes induced by humidity change

Abstract

The stability of underground caverns in Longyou Grottoes is greatly influenced by humidity change since they are mainly composed of argillaceous siltstone, which is highly sensitive to moisture. In this work, a coupled humidity diffusion-fracture model based on the finite-discrete element method (FDEM) is employed to study the fracture characteristics and failure mechanism of underground caverns No.4 and 5 in Longyou Grottoes caused by humidity change. Firstly, the input parameters are calibrated with uniaxial compression tests on dry and saturated siltstone samples. Then, the crack patterns of a disk rock specimen under drying and wetting conditions are captured, which are compared with experimental results to validate the coupled model and calibrated parameters. Subsequently, numerical models of caverns No.4 and 5 in the Longyou Grottoes are established based on the actual geological conditions. The failure processes of the surrounding rock under moisture evaporation and absorption are simulated, and the stress evolution caused by humidity change is analyzed. Results indicate that the caverns primarily experience tensile failure under the evaporation condition with a distribution of tensile cracks perpendicular to the cavern boundary. However, shear failure occurs in the surrounding rock during moisture absorption, and the cracks gradually propagate into the deep rock with humidity diffusion. Additionally, several factors influencing cavern failure are discussed, and the number of cracks is quantified. Finally, it is found that the HDZ of the caverns is significantly reduced by applying a waterproof layer. The findings in this study have practical significance for predicting and improving the long-term stability of underground caverns in Longyou Grottoes under complex climatic conditions.