Abstract:

A three-dimensional rough structural surface characterization was carried out based on the Weierstrass-Mandelbrot (W-M) fractal function. The effects of typical W-M geometric parameters on the three-dimensional surface morphology were discussed. The two-dimensional and three-dimensional W-M geometric parameters corresponding to typical Barton JRC curves were analyzed and provided. Experimental fracture seepage tests on specimens with different fractal parameters and fracture aperture were conducted using a self-designed fracture seepage system based on 3D printing technology. The test results showed that the fluid flow exhibited obvious nonlinearity with increasing hydraulic gradient and roughness. The coefficients of A and B in the Forchheimer equation increased with increasing fracture roughness and decreased with increasing fracture aperture. Meanwhile, the critical Reynolds coefficient tended to decrease as the roughness increased, indicating a tendency towards non-Darcy flow. The analysis of fluid flow patterns revealed that the flow velocity of the smooth structure surface of the model was relatively uniform. The flow field of the rough surface was complex showing several high and low flow velocity regions along the rough surfaces. The research results provide reliable analytical methods and models for the study of fracture seepage characteristics.

Key words: rock fracture, seepage test, fractal dimension, roughness, 3D printing