Both mechanical and hydraulic behaviors of rock joints are closely dependent on joint aperture. Understanding how fracture wall-roughness affects fluid flow is important when modeling many subsurface problems. In this paper, a new evaluation method of joint hydraulic aperture using surface asperities height is developed, and the value of hydraulic aperture under different shear displacements is determined using the multi-scale wave decomposition method based on the wavelet theory and some statistical indices. For this purpose, a high resolution laser scanning system is applied. The numerical simulations are based on the experimental data obtained by Sharifzadeh (PhD, Kyushu, 2004) from a series of hydro-mechanical shear tests on natural granite rock joints. Using this method, the hydraulic aperture of joint surfaces has been developed for different shear steps to model the fluid flow of rock joints. The modeling procedure of mechanical aperture (or dilation) is precise and reliable. In addition, the proposed procedure appropriately estimates both hydraulic aperture and fluid flow rate. The conformity in the results of modeling and laboratory tests satisfactorily indicates success of the proposed procedure.

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