Assessment of bridge scour in the lower, middle, and upper Yangtze River estuary with riverbed sonar profiling techniques
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Riverbed scour of bridge piers can cause rapid loss in foundation strength, leading to sudden bridge collapse. This study used multi-beam echo sounders (Seabat 7125) to map riverbed surrounding the foundations of four major bridges in the lower, middle, and upper reaches of the 700-km Yangtze River Estuary (YRE) during June 2015 and September 2016. The high-resolution data were utilized to analyze the morphology of the bridge scour and the deformation of the wide-area riverbed (i.e., 5–18 km long and 1.3–8.3 km wide). In addition, previous bathymetric measurements collected in 1998, 2009, and 2013 were used to determine riverbed erosion and deposition at the bridge reaches. Our study shows that the scour depth surrounding the bridge foundations progressed up to 4.4–19.0 m in the YRE. Over the past 5–15 years, the total channel erosion in some river reaches was up to 15–17 m, possessing a threat to the bridge safety in the YRE. Tide cycles seemed to have resulted in significant variation in the scour morphology in the lower and middle YRE. In the lower YRE, the riverbed morphology displayed one long erosional ditch on both sides of the bridge foundations and a long-strip siltation area distributed upstream and downstream of the bridge foundations; in the middle YRE, the riverbed morphology only showed erosional morphology surrounding the bridge foundations. Large dunes caused deep cuts and steeper contours in the bridge scour. Furthermore, this study demonstrates that the high-resolution grid model formed by point cloud data of multi-beam echo sounders can clearly display the morphology of the bridge scour in terms of wide areas and that the sonar technique is a very useful tool in the assessment of bridge scours.
KeywordsBridge scour Riverbed erosion Channel morphology Bridge foundation Multi-beam echo sounders The Yangtze River Estuary
During the preparation of this manuscript, Shuwei Zheng was supported by an award of the China Scholarship Council (File No. 201606140126). We would also like to thank an anonymous reviewer for reviewing the manuscript and offering many helpful suggestions, which have helped improve the quality of this paper.
This study was financially supported through a grant from the Natural Science Foundation of China (Grant No. 41476075) and a grant from the Impact of Major Projects on the geological environment of the Yangtze River (Grant No. DD20160246). The study also benefited from a US Department of Agriculture Hatch Fund project (Project No. LAB94230). The statements, findings, and conclusions are those of the authors and do not necessarily reflect the views of the funding agencies.
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