A Study on Flow Characteristics below Bridge Considering Debris Accumulation .

Sung Joong Kim, Do Jun Jung, Joon Gu Kang, Hong Koo Yeo, Yong Uk Ryu

Tuesday 30 june 2015

12:36 - 12:39h at Africa (level 0)

Themes: (T) Water engineering, (ST) Experimental facilities and instrumentation, Poster pitches

Parallel session: Poster pitches: 5F. Engineering - Instrument

This study aimed at examining debris effects on hydraulic characteristics around structures in small rivers targeting small bridges during flood. Although river flows give significant direct impact on structures, indirect ways such as debris accumulation around bridge piers causing the increase of the drag force needs to be considered. In this study, a full-scale experiment of debris accumulation around a bridge pier was conducted in order to understand a feasible cause for damages on small river structures in Korea. For the full-scale experiments, a 1:1 scaled model based on the small bridge standards was installed. The channel where the bridge model was installed is of natural and full scale type satisfying the small river standards. For debris accumulation during the experiments, actual debris of herbaceous plants were seeded upstream. The size of herbaceous plants were determined to meet the general scale for small rivers, which gives an idea for the features of the debris accumulation shapes. In this test, the relation among flow characteristics, debris accumulation, and the damage or failure mode of the structures were examined. In addition to the real scale experiments, detailed investigations for the flow characteristics in the vicinity of the bridge structure were carried out in a smaller scale experimental setup (i.e. the scale ratio of 1:12). The experimental results indicate that the maximum flow velocity occurs mainly below the bridge, which could be due to the reduction of the bridge cross-section. The maximum flow velocity along the water column was observed to occur near the free water surface under the condition of low water level. On the other hand, in case of high water level (i.e. the water level reaching the upper plate of bridge), the maximum flow velocity is shifted toward a lower position, which is likely due to the disturbance by the the upper plate of bridge.