Seeing the scouring phenomenon from the geotechnical perspective/ 洗掘という現象を地盤工学的にとらえる

Partial scour around the basement of the bridge pier is one of the critical incidents that is caused by a flood. Although some empirical design procedures and countermeasures are established, they are not fully composed systematically. As of now, the scouring phenomenon is approached from a hydraulic view which focuses on the intensity of flow (action). The objective of the study is to grasp the dynamic scouring by analyzing the subsoil condition such as density, grain distribution.


Model test / 模型実験

Experiments using the model pier are performed on two scales.
…[Small tank] Width: 0.3m, Length: 2m

Poorly graded gravel, silica sand #7, and a mixture of them are chosen as a subsoil. The relative density of the subsoil is uniformed in any cases. Varying the material type, the effect of the subsoil is analyzed by comparing the change of reaction forces on the bottom of the pier, top displacement, required time to collapse.
…[Large tank] Width: 1.2m, Length: 30m

Only poorly graded silica sand #4 is chosen as a subsoil. The shape of the pier, the angle which the pier faces against the flow, and with or without countermeasures are different in each case. In this large tank experiment, we mainly pay attention to the variables that govern the dynamic procedure of the scouring phenomena, like water level or flow velocity.




Figure 1. 小型水路[small tank]

Figure 2. 大型水路[large tank]