Dry granular flow interaction with dual-barrier systems

Multiple barriers are commonly installed along predicted geophysical flow paths to intercept large flow volumes. The main criterion for multiple-barrier design is volume retained. The velocity of the incoming (far-field) undisturbed flow is also sometimes used, although this neglects the influence of other obstacles on the flow characteristics. This study investigates the influence of upstream flow– barrier interaction on downstream runup and impact mechanisms of a dual rigid barrier system. Four physical flume tests were performed using dry sand to investigate flow interaction with dual barriers. Moreover, three-dimensional finite-element simulations were conducted to back-analyse the flume tests and to investigate the effects of upstream barrier height and barrier spacing on downstream impact characteristics. Two key interaction mechanisms that alter downstream flow are identified: (a) flow momentum redirection (i.e. runup) at the upstream barrier, reducing pre-impact momentum at the downstream; and (b) downstream flow-thinning. Runup mechanisms at the upstream barrier and flowthinning between the two successive barriers have profound effects on dynamic impact pressures at the downstream barrier. When the upstream barrier height is taller than twice the maximum flow thickness, flow energy can be dissipated effectively by momentum redirection. The downstream barrier height and design impact pressure can be reduced up to 17% and 35% for dry sand flows, respectively.