Debris–slit interaction considering the particle behavior controls the barrier performance of slit structure retaining dry granular flows

Slit structures are an important mitigation measure against debris flow disasters. Common insight indicates that the size ratio of the slit and particle is a crucial parameter in designing slit structures, and a size ratio of 3–4 is accepted as the best condition. However, the effect of interparticle interaction behavior on the debris–slit interaction is not well understood, but it is important for determining the critical size ratio. For this reason, a series of DEM simulation tests are conducted considering granular flows with different particle sizes while keeping the ratio of slit size to particle size constant. The results indicate that the size ratio is not the only factor that controls the debris–slit interaction. For the same size ratio, the normalized run-up height would be increased by nearly 4 times and the energy breaking efficiency would be decreased by more than 20% when the Savage number is reduced. However, the material capturing efficiency and peak impact force show less variation for the same size ratio achieved by different combinations of slit size and particle size. In addition, it is found that such an effect exerts fewer challenges to engineering design, especially for smaller size ratios (< 3) and smaller Savage numbers (< 0.75).