Damage detection of underwater foundation of a Chinese ancient stone arch bridge via sonar-based techniques

Abstract

The underwater bridge foundation is critical for the structural safety of bridges, especially the ancient ones. Generally, there is no accurate design details stored for most ancient bridges and the damage detection process must be Nondestructive Testing (NDT). This paper applied sonar-based techniques to the damage detection of the underwater foundation of a Chinese ancient stone arch bridge. A multi-beam sounder was used to measure the river bottom topography of the bridge bottom. The bottom sediment and submerged obstacles of the bridge with both sides were scanned to investigate the state of the wooden stake exposed and the appearance of strip stone foundation. The scour situation of the underwater foundation in combination with the results of multi-beam sounding was analyzed. The underwater foundation was scanned by the underwater 3D sonar imaging technology. The testing results show that: (1) It is inferred that the bottom of Gongchen bridge was originally filled with wooden piles. Due to river erosion and ship bottom scraping, the upper part of the wooden piles in the middle hole of the bridge are damaged to some extent; (2) Because of the influence of passing ships, the riverbed of the middle hole of the bridge was sunken, and the wooden piles of the middle hole are seriously damaged, which affects the stability of the expanded foundation of the strip stone; (3) The height difference of the riverbed between the middle hole and the two side holes is obvious, and the significant lateral pressure was generated. Thus, it is easy to cause instability of the wooden pile foundation; (4) The striated stone foundations of the east and west bridge piers of the middle hole are damaged due to the impact of passing ships, partial collapse and defect. In order to avoid instability, repair and reinforcement should be carried out as soon as possible; (5) The sonar-based techniques can detect the damage of underwater bridges structures, so as to provide an important reference for the safety analysis of the bridge structure.