Hiromichi ODAJIMA

Study on the Stability evaluation of the Hydraulic drop bed protection works by moving bed hydraulic experiment

Tokuzou HOSOYAMADA

The hydraulic drop is a type of consolidation works and a river crossing structure that is set up to stabilize the riverbed, maintain the longitudinal and transverse shape of the river.
In this study, I conducted a hydraulic model experiment of a moving bed with a thick ground layer for a falling cork with concrete structure with water tapping, for the purpose of evaluating stability of the bed protection works block in the hydraulic drop. The experimental conditions were roughly classified into two conditions: the flow rate scale was changed and the river bed lowered. As the experimental measurement items, (1) Flow velocity on the bed protection works (2) Pressure from the ground acting to the bed protection block (3) Pore water pressure inside the ground were acquired in chronological order. In addition, from the aspect of the experiment, I taken movie and monitored the flow regime change and the riverbed form change. By conducting experiments under various conditions, I investigated the influence of external force change, flow rate change, riverbed morphology and water surface shape change on the bed protection works block and the displacement / outflow process of the bed protection works block.
Experimental results revealed that the transition of the hydraulic jump position affects the pressure change of the bed protection works block. It was also found that the pressure acting on the protection bed works block and the pore water pressure in the ground increased when the bed was declining. In addition, it was confirmed that the bed protection works block leads to runoff due to collapse of the foundation ground of the bed protection works block by riverbed scour.