Abstract: Since the catastrophe of the red-bed soft rock is closely related to the water-rock interaction on the surface, the research on the interface process is of great significance to reveal its catastrophic mechanism. However, at present, the study on the red-bed soft rock softening mainly focuses on the macroscopic phenomenological characteristics, and the study on its interface process is still in the exploration and initial stage, which needs further improvement. The characteristics of the interface process of the red-bed soft rock softening are analyzed, which shows the soft rock particles on the water-rock interface are continuously dissolved, and the water diffuses in the soft rock to form a new water-rock interface. Based on this result, the standard entropy of soft rock is established to characterize the soft rock softening, and the evolution of the standard entropy is consistent with that of the softening and disintegration of soft rock over time. At the same time, the dynamics model of soft rock softening interface is constructed by using the Fick diffusion law, which can describe the formation rule of the water-rock interface well. Finally, in the DEM-CFD model of red-bed soft rock, the particle connection fracture in soft rock softening process represents the generation of water-rock interface. Comparing the dynamics models of the interface process, a better fitting result is achieved. The results of this study have certain significance for the exploration of soft rock softening interface.

Key words: red-bed soft rock, softening, interface process, dynamic model, DEM–CFD