Gravity-driven liquid splitting behavior at intersections and its control on infiltration in unsaturated fracture networks

A fundamental understanding of water infiltration in unsaturated fractured rocks is important in a range of subsurface hydrological, environmental and engineering applications. We perform an experimental and modeling investigation of the gravity-driven liquid slug flow behavior at fracture intersections. In the experiments, we visualize the flow processes and quantitatively analyze the flow dynamics. We develop a novel computational model that adequately captures the splitting dynamics. This model considers dynamic contact angles and solves temporal evolution of interface motion based on force balance with the quasi-static assumption at each time step. We systematically examine the influence of various physical parameters on the flow splitting behavior, including the widths and inclination angles of channels, and slug lengths. Using the local splitting relationships obtained mechanistically, develop a network model to study infiltration in unsaturated fracture networks. Then, the influence of the local flow dynamics on large-scale flow structures is systematically investigated. We find that an avalanche infiltration mode emerges spontaneously and that the local splitting relationship controls the divergent and convergent flow structures.