Numerical study on the impact of bouldery debris flows on check dams using a smoothed particle hydrodynamics and finite element method coupled model

Understanding the complicated dynamics of three-phase interaction between matrix fluid, boulders, and structures during the debris-flow impact on check dams is critical to disaster prevention and mitigation. In this study, a smoothed particle hydrodynamics (SPH) and finite element method (FEM) coupled three-phase model is adopted to investigate the dynamics in the impact of boulder-enriched debris flows on check dams. The SPH-FEM-FEM model is first verified in a large-scale flume experiment of debris flows impacting a rigid barrier gate and further applied to investigate the impact of boulder-embedded debris flows on composite check dams with a cushion layer over the upstream surface of the main body. It is shown in the results that the boulders exert resistance on the matrix fluid, and conversely, the matrix fluid forms a buffer layer before the dam to reduce the impact force of boulders. The flexible cushion layer of a composite check dam also reduces the impact force of boulder-enriched debris flows, significantly. Moreover, the flexible cushion layer can remarkably reduce the area of high-stress zones as well as the magnitude of the maximum principal stress in composite check dams. The deformation of the composite check dam surface depends primarily on the stiffness of the materials for the dam cushion layer, more highly on the constitutive property of the cushion materials. The cushion layer composed of sand-gravel soil fulfilling the Drucker–Prager elastoplastic constitutive law leads to a slightly lower impact force and larger dam deformation than that made of the linearly elastic sand-gravel soil.