Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Analysis and research on local scouring of caisson by river bed excavation
Pengpeng Han Xiandao Feng Qihe Wu
CCCC Second Harbor Engineering Company LTD,Wuhan, Hubei, China
Key Laboratory of Large-span Bridge Construction Technology,Wuhan, Hubei, China
CCCC Highway Bridge Construction National Engineering Research Center Co. LTD，Wuhan, Hubei, China
Research and Development Center of Transport Industry of Intelligent Manufacturing Technologies of Transport Infrastructure,
Wuhan, Hubei, China

calculation and protection design. Liu (2012) studied the flow field
distribution of caisson under different flow rates and directions throughnumerical simulation, and made a comparative analysis of scour resultsin model experiment, which showed a good coincidence. Based on theactual project, Liang (2016) analyzed the influence of square and circular
caisson structures on scour depth and the dynamic evolution of scour,and the results showed that scour depth increased with the increase of
caisson diameter. Through normal model experiments, Gao (2015) havestudied the change of scour depth caused by the change of distance fromthe bottom of circular and square caissons to the bed surface. As thebottom of caissons approaches the bed surface, scour depth is locallystrengthened. Chen (2008) established a mathematical model suitable forscour simulation by considering sediment initiation and transport
through the combined force of sediment particle gravity and shear forceof flow. Wang(2017) established a prediction model for scour depth ofbridge pier through theoretical analysis and CFD program development,
which could realize dynamic visualization of scour and proposed theoptimal section shape under the same working condition. Hu(2015) madea comparative analysis of numerical simulation and flume experimentresults, who found that round-end caissons have the lowest flow
resistance and the lowest scour depth under the same width section.
To sum up, previous scholars carried out in-depth studies on the scour
depth of bridge caisson and accumulated a lot of data by using modelexperiments, and obtained abundant research results. Taking the caisson
foundation of Changtai Yangtze River Bridge as an example, this paper
studies the local scour topography of caisson under different flow
velocity, water depth and flow angle . We can keep the river bed flat andreduce the risk of caisson inclination by excavating the foundation pit at
the bottom of the caisson, so as to provide reference for the design ofcaisson landing construction.

ABSTRACT
In order to study the scour morphology of super large caisson foundation
under the river flow, the scour topography was analyzed under differentwater depth, flow velocity and flow Angle. Taking the caisson
foundation of Changtai Yangtze River Bridge as an example, themaximum scour plane position of caisson and the relationship of scour
morphology with time were studied. The results show that the scour
depth increases with the increase of flow. When the water depth is greaterthan 20m, the scour depth does not change with the increase of water
depth. When there is a certain angle between water flow and caisson, themaximum scour depth moves to the end of caisson facing
surface. Because the scour pit formed at the front of the caisson causes
the caisson to sink and tilt, the foundation groove excavated in advanceis beneficial to the leveling of the river bed. For large caisson foundation,
the calculation formula of scour depth at home and abroad does notconsider the scour influence factors completely, and can only be used
under certain conditions multiplied by the coefficient.

KEY WORDS: Large caisson foundation; Terrain by scouring andsilting; base slot excavation; Formula contrast.

INTRODUCTION
Caisson landing on the river bed is an important risk in the constructionof bridge deep water foundation. When the caisson is in bed, the waterflow is blocked by the caisson form the descending vortex. the scour pit
is formed in the front of the caisson, which will have caused the safety
accident because of the caisson tilting. Local scour of pier is the result of
the interaction of water flow, sediment and pier, and there are many
problems such as three-dimensional and unsteady state in the process ofstudy. Many scholars have made great efforts to study the law of scour.
Ji(2010)and Pasiok R(2010) obtained the flow field distribution aroundthe cylinder by numerical simulation, which can be divided into
descending flow at the front, compression flow at the middle and eddy
current at the tail, providing important reference for riverbed scour

CEXTION FORN OF CAISSON FOUNDATION
Local scour of caisson is one of the important bases for bridge design,
which can be influenced roughly by flow characteristic, riverbed
sediment and caisson type according to their properties. From 1950s to1547