A Physical and Numerical Investigation of Flow–Barrier Interaction for the Design of a Multiple-Barrier System

Multiple barriers have become popular to mitigate debris flows worldwide. Existing guidelines only recommend the minimum spacing based on volume retention, and the influence of flow–barrier interaction is ignored. It is obvious that understanding the flow–barrier interaction for a multiple-barrier system is imperative for safer and more economical designs. In this study, a physical experiment of debris flow impacting a dual rigid barrier system conducted in a 28-m-long flume is presented. The experimental results are used to calibrate a numerical model based on the lattice Boltzmann method (LBM) with a new Voellmy-like rheology. A numerical parametric study is then conducted to investigate the influence of the barrier heights and of the spacing between the barriers on the overflow mechanisms, the material depositions, and the impact dynamics. A new method to estimate the launching angle using the ratio between the barrier height and the flow thickness is proposed to calculate the overflow distance $L^{+}$. Furthermore, the existing volume retention criterion can be used when spacing $L$ is between 2 and 5 times the overflow distance $L^{+}$ (i.e., $L/L^{+}\approx 2–5)$ and both barriers have a similar height. Whereas, when $L/L^{+}>10$, a smaller first barrier results in reduced impact force due to flow thinning and spreading between barriers.