Abstract: The surface morphology of rock mass cracks is constantly changing under complex stress and long-term seepage erosion, which leads to more complicated evolution mechanism of seepage characteristics of rock mass fissures. The fluid flow experiments in different roughness limestone fractures were conducted. The effect of coupled stress-fluid flow erosion on the surface morphologies of rough fractures was analyzed according to the experimental results and the comparison of fractures surface morphology characteristics before and after fluid flow experiments, and permeability evolution of rough rock fractures was studied. The results show that the seepage discharge of different roughness fractures decreased rapidly in the initial stage of the experiment and then tended to stable with time under the action of stress. The equivalent hydraulic aperture and permeability of different roughness fractures were approximately equal in the initial stage of the experiment, and then continue to decrease. But under the coupling of stress and seepage erosion, the fractures surface was rougher, the decrease amplitude of equivalent hydraulic aperture and permeability was greater, the stable value was smaller at the end of the experiment. The fracture with small roughness had uniform seepage path and straight streamline, while the fracture with large roughness appeared groove flow and its seepage path was more tortuous and extended. The more the number of convex bodies on the fractures surface was, the greater the area for fluid flow was, and the stronger the erosion modification effect of stress and seepage erosion on the fractures surface morphology was. The above change of surface morphology aggravated the groove flow of the fracture surface and affected the permeability evolution of fractures in turn.

Key words: rock fracture, permeability, stress-seepage erosion coupling, roughness coefficient