Nature-friendly hydraulic structures such as a rubble mound weir have attracted researcher's attention in recent years. Therefore, it is important to establish a numerical model to predict a possible failure process. In this research, the distinct element method which is used for modeling the aggregate of discontinuous elements is applied to model a failure process of the rubble mound weir. Hydrodynamic forces acting on the rubble-mound weir such as drag force and seepage force which are required in the calculation of DEM was obtained by the flow analysis using VOF technique. It is confirmed that the numerical results using the proposed method can reproduce the movement of particles in the early stage of failure under the steady flow condition. It is also clarified that the contact angle of DEM particles has a significant effect on the failure process.
After dam construction, the flow and sediment regime change downstream from the dam. For example, the armor coat progresses because of sediment trapping by the dam. To solve these problems, 'sediment replenishment' has been executed recently. Nevertheless, it is difficult to maintain effects of sediment replenishment over the long term because the restored sediments are washed away easily in steep rivers, especially in slippery bedrock sections. Therefore, the authors have proposed techniques that promote gravel sedimentation by improving riverbed forms. The effects of proposed techniques such as the river widening and multistep masonry weirs were investigated using a two-dimensional numerical model. Results showed that the proposed techniques are useful to reduce tractive force in steep rivers. They can create a desirable bed state for river ecosystems with various gravel sizes.
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