Experiments with Non-Darcy Flow in Joints with Large Scale Roughness

摘要

Joints are normally in contact at roughness asperities; consequently the relative roughness, the ratio of the asperity protrusion to the mean flow aperture, is approximately one, which is orders of magnitude greater than that encountered in more usual situations such as pipe and channel flows. In our experiments the joint roughness was idealized with sawtooth corrugations. We found that Darcy's Law became invalid for Reynolds numbers greater than about 100. Hence, for most of our studies the flow was non-Darcian, and so we adopted the usual convention of representing pressure losses in terms of an apparent friction factor. When the roughness peaks were aligned, resulting in maximum flow disturbance, the friction factor increased when the relative roughness was increased, simulating the closure of a joint due to normal-direction loading. However, when the roughness peaks were 180 deg out of phase, so that peaks were opposite valleys, the friction factor initially increased with greater relative roughness, but then decreased. 2 refs., 8 figs., 2 tabs. (ERA citation 10:045289)