Debris flow impact on flexible barrier: effects of debris-barrier stiffness and flow aspect ratio

Abstract

Conventionally, flexible barriers are rated based on their ability to resist a free-falling boulder with a particular input energy. However, there is still no well-accepted approach for evaluating performance of flexible barrier under debris flow impact. In this study, a large-nonlinear finite-element model was used to back-analyze centrifuge tests to discern the effects of impact material type, barrier stiffness, and flow aspect ratio (flow height to flow length) on the reaction force between the impacting medium and flexible barrier. Results show that, in contrast to flexible barriers for resisting rockfall, the normal impact force induced by the highly frictional and viscous debris is insensitive to barrier stiffness. This is because the elongated distributions of kinetic energy are mainly dissipated by the internal and boundary shearing, and only a small portion is forwarded to the barrier. Furthermore, a new stiffness number is proposed to characterize the equivalent stiffness between a debris flow or a boulder, and a flexible barrier. Under the circumstance of an extremely elongated debris flow event, i.e., low aspect ratio, the load on a barrier is dominated by the static component and thus not sensitive to the barrier stiffness.