Experimental evidence of scale-dependent hydraulic conductivity for fully developed turbulent flow in a single fracture

SummaryThis study uses laboratory experiments to investigate scale dependent hydraulic conductivity of fully developed turbulent flow in a single fracture under different fracture surface roughness, fracture apertures, and hydraulic gradients. The hydraulic conductivity for fully developed turbulent flow is defined as K = V2/J, where V and J are absolute values of the flow velocity and the hydraulic gradient, respectively. Three different surface roughness (fine, medium, and coarse), three different fracture apertures (1.0 mm, 2.0 mm, and 2.5 mm), and five different hydraulic gradients have been tested. Experimental evidence shows that K values generally increase with scale in a linear fashion. Surface roughness and fracture apertures appear to have the most significant influence upon the scale-dependency of K, which is less sensitive to hydraulic gradients. In general, a higher hydraulic gradient will lead to a lower K value at a given scale. The scale-dependency of K might be a manifestation of two-dimensional torturous flow within a rough surface fracture.