Rock mass contains various discontinuities in terms of size and shape, such as fault, joint, and bedding plane. Among them, a joint is a planar discontinuity that has little strength and it shows smaller size but more frequency than a fault. In general, the joint exerts huge influence on mechanical behavior of rock mass since it acts as a weak plane. At the same time, the joint has several orders higher hydraulic conductivity that rock matrix so that the majority of fluid flow in rock mass occurs through the joint. Therefore, accurate understanding of characteristics of a rock joint is of great importance, as it affects both mechanical and hydraulic behavior of rock mass. Not only the mechanical conditions but also the geometric features affect the joint behavior. The geometric features can be explained by various properties, such as roughness, aperture, contact area, and so on. They exert complex influence on the hydromechanical characteristics of a joint, interacting with each other. Therefore, a series of laboratory experiments were conducted in order to investigate the hydraulic characteristics under various mechanical and geometric conditions. A fractal theory was used to generate coordinates of artificial rock joint surfaces so as to control the roughness of the joint. Then the coordinates were printed by a 3D printer and utilized to make cement mortar specimens. Four joint specimens, which had different levels of roughness and aperture, were prepared and tested. Before investigating the hydraulic characteristics, mechanical behavior of joint specimen was tested first. In order to consider various mechanical conditions, normal and shear stresses were applied and hydraulic tests were conducted with the same mechanical and geometric conditions. The results showed that flowrate per unit hydraulic head decreased with the increase of normal stress, increased with the shear displacement, and increased with the roughness of the joint. Also, comparison between hydraulic aperture, which was calculated based on the cubic law, and corresponding mechanical aperture was made and it showed more deviation from the cubic law when the roughness and stress were increased.

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