Explore the influence of fracture void space geometry on seepage: The effect of cross-sectional area and the blockage of contact area

Abstract

The cross section of a fracture along the streamwise direction determines the water-passing capacity of the fracture. The seepage fields in four fracture models with different contact conditions are analyzed and investigated via computational fluid dynamics simulations. The main results are as follows: (1) a kind of low-velocity region is formed under small local aperture conditions; (2) the blocking degree of the contact area to the fracture seepage depends on the local flow channels compressed by it (flow angle and local aperture); (3) on a cross section, the interference of the contact area and roughness on the fluid flow make the average flow velocity (Uavg) greater than its streamwise component (uavg) except for seepage inlet, which increases with the decrease in the average mechanical aperture and the expansion of the contact area [C = 17.90%, compared to lower C, the whole average flow velocity (1.88 m/s) is the maximum]; (4) there may be an upward trend of pressure along the streamwise direction: where the cross-sectional area increases, the additional kinetic energy generated by the reduced flow velocity will be converted into pressure potential energy if it is not fully consumed by the viscous force; (5) along the streamwise direction, there is a linear correlation between the change rate in uavg (∂uavg/∂x) and that of average pressure on a cross section (∂P/∂x), which is affected by the interference of the contact area and roughness (R2 = 0.25 at C = 17.90%), a conceptual model derived from this linear correlation can describe the relation between the hydraulic characteristics of a fracture and streamwise cross section.