Microfracture behavior and energy evolution of heterogeneous mudstone subjected to moisture diffusion

Moisture has a great effect on the microstructure of mudstone and the stability of muddy strata. Due to many clay minerals in mudstone, swelling deformation and even disintegration occur during moisture diffusion, accompanied by energy storage and release. To reveal the deterioration mechanism and energy characteristics of mudstone induced by moisture diffusion, firstly, the Weibull distribution function is introduced into the FDEM-based moisture diffusion-fracture coupling model to consider the heterogeneity of swelling deformation and stress of mudstone minerals. Then, the microfracture behavior and energy evolution of heterogeneous mudstone during moisture diffusion are studied using the coupling model. Results indicate that the nonuniform swelling deformation between particles is the main reason for the microfracture, both tensile and shear failures occur in mudstone. The evolution of kinetic energy can be divided into three stages, while that of strain energy depends on the storage rate by swelling deformation and the release rate by microfracture in mudstone during moisture diffusion. When the storage rate is greater than the release rate, the evolution of strain energy is divided into two stages. Otherwise, it is divided into three stages. Besides, the effects of homogeneity index, swelling coefficient, and moisture content on the microcrack morphology and energy evolution are also discussed. Finally, the microcrack morphology and energy evolution of mudstone under different moisture loading conditions are investigated, where the microcrack morphology under the surrounding moisture condition agrees well with the experimental results. The results in this paper provide theoretical value for studying the swelling and microfracture mechanism of mudstone during moisture diffusion.