Impact of water–rock interaction on the pore structures of red-bed soft rock

The physical and mechanical properties of the reservoir bank slope are affected by the water–rock interaction. However, few studies considered the impact of long-term water–rock interaction on the evolution law of mesostructure. Therefore, in this study, the water–rock interaction test was conducted on a slightly weathered red-bed soft rock from the Three Gorges Reservoir area, considering the fluctuation in the reservoir water level. The corresponding pore structure parameters were measured and analyzed based on a scanning electron microscope (SEM) and digital image processing technology. The study showed that: (1) The pore size has been gradually increased, while the number of pores was increased initially and then decreased. Within 12 cycles, the maximum and average pore radius of the rock specimens was increased by 101.02% and 43.32%, respectively, and the porosity has been increased by 26.59%, whereas the number of pores decreased by 22.65%. This indicates the effect of water–rock interaction on the propagation of pores. (2) The pores were changed from oblate to slender by the water–rock interaction. The shape factor was decreased by about 15.79% within 12 cycles. In the meantime, the fractal dimension was increased from 1.20 to 1.28, and more complex structures of pores were observed. (3) The porosity evolution model for the red-bed soft rock was established based on the curve fitting technique. The results can be used as a reference to conceptualize the mesostructure damage of rocks under water–rock interaction.