Experimental studies of water seepage and intermittent flow in unsaturated, rough-walled fractures

Flow visualization experiments were conducted on a transparent replica of a natural, rough-walled rock fracture from the Stripa Mine, Sweden, for inle t conditions of constant pressure and flow rate over a range of angles of i nclination. The experiments demonstrated that infiltrating water proceeds t hrough unsaturated rock fractures along nonuniform, localized preferential flow paths. Even though constant inlet conditions were maintained, pervasiv e unsteady or intermittent flow was also observed in these experiments, whe re portions of the flow channel underwent cycles of snapping and reforming. Experiments conducted on parallel plates with a sequence of apertures prog ressing from small to large to small reproduced intermittent flow. Measurem ents of the frequency of intermittent flow events and the volume of water m etered between events were obtained from the fracture replica and parallel plate experiments and related to the Bond and capillary numbers to generali ze the results. The frequency data from the fracture replica experiments di d not follow the same trend as the data from the parallel plate experiments for similar Bond and capillary numbers, but the volume of water metered da ta was consistent in these experiments.