Wave-Induced Transient Sandy Seabed Response Around A Single Pile Foundation

With the development of the strategies of “One Belt and One Road” and “Ocean Power”,China has ushered in the climax of the construction of Marine structures,especially in the aspect of sea-crossing bridges.Different from inland bridges,sea-crossing bridges are located in a complex environment,and their pile foundations are usually subject to wave loads,which affects the stability of bridge structures.The periodic wave loads can not only cause the damage to the pile foundation itself,but also affect the seabed response around the pile foundation and indirectly endanger the safety of marine structures.In the process of wave propagation,periodic wave loads will be applied on the surface of the seabed,which cause the changes of the stress in the seabed.When the effective stress gradually decreases to zero,the seabed soil will lose its bearing capacity by liquefaction,and thus lead to the instability and failure of the upper structure.Therefore,the study of the seabed response around the pile foundation is of great significance to the safety of marine structures.Based on the established 3-D numerical model and combined with the physical model test,both the transient response and the liquefaction mechanism of seabed are investigated.In this thesis,RANS equation is taken as the governing equation of wave model,and then a wave-structure interaction model has been established by Flow 3D.Besides,a porous elastic seabed model has been established by COMSOL Multiphysics,in which the Biot's poroelastic equation is used to govern the transient soil dynamic response.Combining the wave model and the seabed model,a 3-D numerical model of wave-monopile-seabed interaction has been set up.Compared with the previous analytical solutions and experimental data,the accuracy and reliability of the numerical model are verified.In order to investigate the wave-induced pore pressure response of the seabed around a single pile,physical model tests have been carried out.According to the test data,the variation of pore water pressure around a single pile along the wave propagation direction,along the depth direction of the seabed and along the circular direction of the pile are analyzed.Base on the established 3-D model of wave-monopile-seabed interaction,the distributions of pore water pressure around a single pile under wave action have been studied.The seabed liquefaction mechanisms around the monopile foundation under wave action have been investigated.The effects of wave parameters and mono-pile diameter on wave-induced oscillatory soil response have also been examined respectively.In addition,a formula for calculating the maximum liquefaction depth around a single pile has been fitted according the results of numerical simulation and liquefaction criterion,which can provide references for practical engineering.