Abstract
Tsunamis can destroy bridges in coastal areas. Studies have attempted to unravel the mechanism of tsunami-induced damage and develop effective countermeasures against future tsunamis. However, the mechanisms of tsunami-induced erosion of bridge-abutment backfill and its countermeasures have not been studied adequately. This study investigates this topic using numerical analysis. The results show that the tsunami flowing down along the downstream wing of the abutment induces bedload sediment transport on the ogive section of the backfill on the downstream side of the abutment, resulting in the onset of backfill erosion. Sediment suspension and bedload sediment transportation occur when the backfill inside the abutment starts to flow out from below the downstream wing. This leads to subsidence of the backfill at the upstream side of the downstream wing. The subsequent backfill erosion is mainly caused by bedload sediment transport. Numerical experiments on countermeasures show that extending the wings downward can prevent the acceleration of backfill erosion in the presence of the abutment. A combination of multiple countermeasures, including extended wings, would be more effective in maintaining the stability of the abutment after a tsunami. This suggests the application of such countermeasures to actual bridges as an effective countermeasure against backfill erosion.
Highlights
Structures in coastal areas suffer severe damages due to tsunamis
Several forms of structural damage were observed during the 2004 Indian Ocean and 2011 Tohoku earthquake tsunamis, including the overturning and wall failure of reinforced-concrete buildings in coastal areas, local scouring around their foundations, separation of concrete panels and armor blocks of coastal dikes, collapse of seawalls and flood walls, washaway of roadways and railway bridge superstructures, failure of bridge piers, and damage induced by impact and damming of debris such as shipping containers, vessels, timber logs, boulders [1,2]
The mechanism of tsunami-induced backfill erosion of bridge abutments and its countermeasures were investigated through numerical analyses based on FS3M
Summary
Structures in coastal areas suffer severe damages due to tsunamis. For example, several forms of structural damage were observed during the 2004 Indian Ocean and 2011 Tohoku earthquake tsunamis, including the overturning and wall failure of reinforced-concrete buildings in coastal areas, local scouring around their foundations, separation of concrete panels and armor blocks of coastal dikes, collapse of seawalls and flood walls, washaway of roadways and railway bridge superstructures, failure of bridge piers, and damage induced by impact and damming of debris such as shipping containers, vessels, timber logs, boulders [1,2]. Nakamura et al [5] investigated the tsunami-induced pressure and load acting on a bridge superstructure using hydraulic model experiments and numerical simulations based on the hydraulic model They used the results to propose estimation formulas for the temporal changes in the horizontal and vertical forces. Inoue et al [8] and Yoshizaki et al [9] conducted centrifuge model experiments to investigate the erosion of two types of abutments These studies demonstrated the sliding of the slope of the backfill, especially on the downstream side, despite little damage to the crown because of an increase in wave pressure, and the average slide height relative to the initial backfill height was correlated with the velocity of the leading edge of the tsunami.
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