Fractal Characterization of the Microstructure of Red-Bed Soft Rocks and Kinetic Modeling of Interfacial Evolution

The deterioration mechanism of red-bed soft rock is attributed to microstructural changes induced by water–rock interactions, where the damage to pores and the development of fractures significantly impact its macroscopic mechanical performance. The microstructural deterioration pattern of red-bed rock with different water saturation times was obtained by scanning electron microscopy (SEM), which showed that the microdamage effect of mudstone is an evolutionary process comprising the dissolution and detachment of its internal soluble bond structure. Three-dimensional (3D) images of the water-saturated damage of the rock mass were extracted by computed tomography (CT) scanning and calculated based on the box-counting algorithm to obtain the fractal dimension of the fracture development, leading to the theory that a soft rock fracture has multiple fractal characteristics. With the continuous increase in the water saturation time, the pores inside the rock mass began to reorganize and connect, and the mudstone specimens showed accelerated damage and some self-similarity. Furthermore, chemical element testing was conducted on the solutions used for water saturation, leading to the establishment of a microscopic interfacial evolution model describing water–rock damage, with theoretical equations derived based on diffusion theory.