Forensic Diagnosis on Flood-Induced Bridge Failure. I: Determination of the Possible Causes of Failure

Abstract

In Taiwan, many bridges span rivers that exhibit severe channel variations in response to drastically increased flows and resulting floods caused by typhoons and storms. Flood-induced scour can undermine the effective embedment depth of bridge foundations. The Shuang-Yuan Bridge, spanning a downstream section of the Kaoping Stream, was severely damaged during Typhoon Morakot in August 2009. A qualitative investigation was conducted to determine the possible causes of this bridge collapse. Relevant hydrologic, meteorologic, structural, geotechnical, and terrain information from various sources both in written and image formats was collected, updated, and reviewed. The disaster investigation included field investigations, nondestructive inspection of bridge remnants, and investigation of structural damage of upstream river crossings, hydrologic changes, damage to training structures/embankment, riverbed profile changes, and debris during the flood event. Several inspections were applied to determine the embedment depths, positions of underwater remnants, and changes in riverbed elevation. The investigation results identified multiple possible causes of failure, including flood flows, river-bend-induced turbulent flows, and the joint effects of extended foundations and rafted wood.