【作者】 潘冬子；

【导师】 王立忠； 潘存鸿；

【作者基本信息】 浙江大学 ， 岩土工程， 2007， 博士

【摘要】 波浪引起的海床变形和稳定性问题是海底管线工程设计中必须考虑的关键问题之一。研究波浪荷载作用下海床及管线的动力特性，对于海床及管线的稳定性评价具有重要意义。基于这样的出发点，按照国家自然科学基金资助项目“海底管线灾变机理及TDR监控研究(No.50479045)”的总体要求，本文采用理论分析、模型试验和数值模拟相结合的方法，对海床及管线波浪响应的基本问题进行研究，揭示了一些现象的力学机制，为工程设计提供可参考的依据。分别基于平面应变条件下的Biot固结理论和广义Biot固结理论，采用积分变换的方法，求解突加波浪荷载作用下单层海床的动力响应问题，并利用Frobenius级数解对Gibson海床的波浪响应问题进行研究。结合大量的算例，针对波浪荷载作用下海床的孔压响应、应力场分布及土骨架位移等问题进行了详细地分析，并与前人的工作进行了对比。增设覆盖层是海床保护常用的措施之一。对于成层海床的波浪响应问题利用状态空间法进行分析，建立表征该问题基本状态量之间的传递矩阵，通过矩阵递推规律、边界条件及逆变换技术实现成层海床波浪响应问题的求解，并对成层横观各向同性海床和海床—土工布复合体系的波浪响应问题进行研究。分析结果表明，覆盖层能有效的提高海床抗剪切破坏和抗瞬时液化的能力，起到保护海床的作用。利用大型波浪水槽通过机械造波分不同的工况进行波浪荷载作用下海床及管线的动力响应模型试验研究。结合试验数据，利用信号分析的方法，探讨了波浪荷载作用下海床孔压发展的机理，对土工布加固粉质海床进行了模拟试验；深入系统地研究了推进波作用下管线周围局部冲刷的演化规律和冲刷形态；对于浅埋管线，通过不同工况的模型试验研究加载波浪周期、波高、相对水深、散射系数及相对埋深等参数对管线周围孔压和管线所受上举力的影响。结合波浪水槽模型试验的结果，分别利用保角变换法和基于贴体坐标的有限差分法，对波浪—海床—管线的相互作用问题进行分析，讨论管线存在对于海床孔压场、应力场和位移场的影响，进而对管线周围局部区域剪切破坏和瞬时液化特性进行分析；并采用状态空间法和共振条件求解波浪荷载引起的海底管线极限冲刷长度，讨论了地基模量、管径、施工残余轴向力及共振频率对极限冲刷长度的影响。对波浪引起的海床表层液化进行研究，提出了分析表层液化的启动和发展深度的判据，在此基础上从信号分析的角度入手，采用多尺度分析法对波浪荷载引起的海床累积液化进行分析，并通过基于贴体坐标的有限差分法实现波浪—海床—管线的液化评估。更多还原

【Abstract】 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.更多还原