Semi-Analytical Procedure for Considering Roughness Effect on Hydraulic Properties of Standard JRC Profiles

In most practical applications, water flow within the rock joints (rough surfaces) is simulated as laminar flow through two smooth parallel plates and cubic law is used for estimating flow rate. In this simulation, a constant opening is assumed between upper and lower parallel surfaces (hydraulic aperture) that will allow passing of the same volume of water flow through real joints. Roughness on rock joints produces variable aperture across the joints and increases the flow path length. These facts affect water flow within rock joints. Therefore, the validity of cubic law is in dispute and depends on accuracy of the hydraulic aperture estimation. In this study, the concept of local true aperture and tortuosity is applied to assumed joints where surfaces are matched to each other and correspond with standard Joint Roughness Coefficient (JRC) profiles. The local true aperture through the joint profile is computed for each JRC profile. A new equation is introduced between mechanical and hydraulic aperture for different JRC values.