Effect of slit size on the impact load against debris-flow mitigation dams

Structural countermeasures such as slit dams and check dams are widely installed in mountainous regions to mitigate debris-flow hazards. However, current approaches adopted to estimate debris-flow impact load only depend on the flow properties without considering the effect of structural geometry. To better understand the effect of slit size on the impact load experienced by debris-flow mitigation dams, a series of small-scale debris flows impact tests on modelled slit dams and check dams are conducted in an instrumented flume. Measurement of the flow velocity, depth, impact load, total basal normal stress, and basal pore-fluid pressure enable a comprehensive grasp of the impact details. Tests reveal that the peak frontal impact pressure is largely unaffected by the slit size of structural countermeasures but is sensitive to the debris-flow properties. However, the slit size obviously influences the peak force experienced by the structures. A critical relative slit size (ratio of slit size to the maximum particle diameter in the debris flow) of 3.6 is determined wherein slit dams can effectively mitigate debris-flow hazards. In addition, a simplified bilinear pressure distribution model is proposed for debris-flow impact load estimation of the slit dams and check dams.