The hydraulic characteristics of the rock mass are of great importance in many rock engineering projects. Various factors affect the characteristics, but in this study, the effect of roughness on hydraulic conductivity was investigated by a series of experiments. Based on the fractal theorem, and controlling roughness of a rock joint with 3D printing technology, we investigated the variation of hydraulic conductivity of a single rock joint. Two levels of joint roughness were tested under various water and normal pressures. As a result, a relationship between hydraulic conductivity and rock surface roughness is proposed.


The hydraulic characteristics of the rock mass are of great importance in many civil and mining engineering projects such as grouting (Barton and de Quadros, 1997), oil/gas production (Wu, 2002), geothermal energy (Min, Rutqvist, and Elsworth, 2009) and tunnelling. The hydraulic characteristics of the rock mass normally interact with the mechanical conditions of rock discontinuity, therefore the coupling behaviour between them should be taken into account. However, in general, investigating this experimentally requires quite complex procedures, therefore the investigation variation in hydraulic properties according to various mechanical conditions has frequently been adopted in many previous studies (Brown, Caprihan, and Hardy, 1998; Lee and Cho, 2002; Singh, Singh, and Ranjith, 2015).

In most rock engineering projects, fluid flow occurs mainly through rock discontinuities. Therefore, many experimental studies have focused on fluid flow in a single rock joint. Fluid flow through a joint can be affected by many factors, such as roughness, aperture, stiffness of joint surface, infilling material, and so on. Among these, aperture and roughness, which are closely related, are known to be highly influential. Roughness is usually controlled in the studies because of its relative simplicity. Nonetheless, controlling roughness requires excessive effort in terms of sample preparation because a joint surface having a desired roughness is very hard to obtain in ordinary procedures. Recent development in 3D printing technology can be used to overcome this cumbersome procedure since one can obtain any level of roughness using point cloud-type data.

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