Hydrophilic and strength-softening characteristics of clay-rich rocks

To better understand the mechanism of the strength weakening process of clay-rich rocks after interacting with water, the relationship between mineral composition, microscopic pore structure and gaseous water adsorption characteristics of clay-rich rocks was comprehensively analyzed by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and mercury injection test. The results show a positive correlation between water absorption and both clay minerals and montmorillonite (MMT) content. The more complex the microporous structure is, the more pores in the diameter of 0.2 ~ 2µm accumulated, and the worse the water absorption capacity obtained. The innovation of this study lies in quantitatively calculating the weight coefficients of influencing factors, highlighting the contribution of pore structure and hydrophilic mineral composition to the strength of clay-rich rocks samples after water absorption, which was not covered in previous studies. The results show that the weight coefficients are fractal dimension of pores, effective porosity and clay mineral content in order. The clay minerals content is negatively correlated with the strength of the clay rocks after water absorption, that is, the presence of MMT is the key influencing factor of strength softening in this study, and the paper concludes with the results of molecular dynamics (MD) simulation to illustrate more intuitively the effect of hydrated MMT on strength. The research results provide a new insight to better understand the strength softening caused by water sensitivity of clay-rich rocks and to establish the correlation between the macroscopic mechanical behavior and the micromechanical mechanism.