Dynamic Response Of Seabed And Pipeline Due To Wave Loading

Wave-induced deformation and destabilization of seabed is a key question for geotechnical engineers involved in design of submarine pipelines. It's very important to study dynamic response of seabed and pipeline due to wave loading for evaluating the stability of foundation and pipeline. According to the total scheme of program supported by NSFC, the catastrophic mechanism of submarine pipeline and TDR monitoring and controlling (No.50479045), this thesis presents the results of recent investigation. Mechanical explanations about some problems are presented combined with theoretical analysis, model test and numerical modeling method, and this may provide assistance for engineering design.By employing an integral transform method, transient solution for wave-induced seabed response are gained based on Biot's theory and generalized Biot's theory, and Frobenius method is utilized for Gibson seabed, respectively. The response of pore pressure, stresses and displacement in seabed are studied in detail by examples, and the present analytical solution can be checked by the previous research about this problem.Cover layer usually be placed on the seabed to protect them from wave action. State space method together with integral transform techniques are used to analysis the response of multilayered seabed due to wave loading, and obtain the transfer matrix which represents the relationship between the basic state vectors in a clearly arranged way. Multilayered seabed can be calculated by using the matrix theory, boundary conditions and inverting integral transform. Wave-induced response of cross-anisotropic seabed and seabed-geotextile system also can be solved by state space method. The numerical calculations suggest that the seabed can be prevented form shear failure and transient liquefaction by placing a layer of gravelly soils on the top of the sandy seabed.Experiment investigations are carried out in a wave flume to study the wave-induced response of seabed and pipeline. The mechanism of pore pressure development in seabed is discussed by signal analysis method based on the experiment date. An improvement method associating geotextile is proposed to strength the silty seabed. Local scour aroundpipeline due to progressive wave is investigated, which contains the local scourmechanism and patterns. The pore pressure and uplift force on a shallowly embedded pipeline is also considered. The influence of various parameters, viz, wave period waveheight, relative water depth, pipeline diameter, scattering parameter, and relative burial depth on pore pressure and uplift force on the pipeline are investigated.After systematic analysis the results of model tests, the conformal mapping method and a finite-difference model in body-fitted coordinate to investigate the wave-induced response of seabed around a pipeline are proposed. The influence of pipeline on the response of pore pressure, stresses and displacements are discussed. Employing Mohr-Coulomb failure and transient liquefaction criterions, the wave-induced seabed instability is also examined. Based on the state space method and resonance term, the extreme erosion length of submarine pipeline under wave loading is presented. Parameters analysis with modulus of foundation, diameter of pipeline, construction residual axial force and resonance frequency is also presented.Superficial liquefaction of seabed due to wave loading is studied, and the criterion for the onset of the liquefaction and the depth of development are gained. Further investigation is proceeding with the signal analysis of the actual measured response of pore pressure from model test. Based on the multiple time scale analysis, the wave-induced response of silty seabed is discussed, and assessment of liquefaction about wave-seabed-pipeline system under waves can be performed with the finite difference model in a body-fitted coordinate.