The force exerted by granular flows on slit dams

Abstract

Boulders often accumulate at the fronts of fast-flowing steep creek hazards. To trap these boulders, slit dams are commonly installed along steep creeks. An outstanding challenge when designing such dams lies in estimating the load exerted by a cluster of boulders: Clusters may exhibit discrete or continuum loading behavior, depending on their size. In this study, a physical flume test was carried out and the obtained results were used to calibrate a discrete element method (DEM) model. The DEM was then used to carry out a parametric study as a function of grain size, slit width and the channel slope. Results reveal that for continuum-like flows, the pressure near the slit of a slit dam can be almost double than elsewhere on the slit dam, as quantified using a newly proposed dimensionless ratio. For discrete flows, impact forces near the slit are more than double than elsewhere, thus representing a critical case for slit dam design. The concentration of forces near the slit necessitates designing for loads 2–3 times that of the rest of the slit dam to avoid wearing. (If wearing occurs, the slit width will increase, along with the volume of discharge, a potentially catastrophic scenario.) Furthermore, two dimensionless weighting coefficients that distinguish pressure from continuum-like flows and discrete impacts are proposed and evaluated. These coefficients can be incorporated into existing analytic expressions used by engineers.