Temporal evolution of the hydrodynamic loading due to dynamic debris jam on bridge pier

Abstract

Woody debris enter rivers during flood events, and the debris is captured and accumulates in the form of a debris jam in front of/around the pier. A woody debris jam can significantly increase the possibility of bridge failure, and it is hence necessary to investigate the mechanism and processes through which the debris is affecting the pier. In this study, physical modeling was conducted to investigate the temporal evolution of debris jam as well as the load and additional hydraulic head caused by the presence of the debris jam. Either dowels or seedling trees were used as debris. The experiment results showed that the horizontal debris jam plan area correlated with the frontal vertical area and this correlation resulted in the development of a method used to estimate the blockage ratio caused by the debris jam in the channel. The drag coefficient caused by the debris jam was also calculated using the measured load caused by the debris jam. In addition, the hydraulic head caused by debris jam was measured during the development of debris jam, and it was found that the hydraulic head was correlated with the blockage ratio and the Froude number. This study provided a spatio-temporal perspective into the development of debris jams.