【作者】 崔嵩；

【导师】 夏小和；

【作者基本信息】 上海交通大学 ， 岩土工程， 2012， 硕士

【摘要】 在海洋岩土工程的研究中,海床,结构物,波浪的相互作用问题,一直是研究的热点之一。海床结构物稳定性的影响因素,主要是海床基础的稳定性,开展对海床稳定性的研究非常重要。海床土体为饱和土,处于复杂的应力作用环境,其稳定性主要表现在受力以后的表面位移,剪切模量的变化,超孔隙水压力响应规律,导致液化致使海床承载力的急剧减小。本文重点研究海床液化问题,基于u-p场控制方程,对固相和液相分别采用有限元法和有限差分法进行离散,推导了两相体耦合动力有限元方程,开发了水土耦合动力有限元计算程序,并在程序中加入了应力诱导各向异性弹塑性模型。随后建立一个多孔介质弹塑性海床模型,通过数值模拟计算,输出海床超孔隙水压力响应结果,按照有效应力理论,判断海床液化深度,分析得到波流共同作用下砂质海床动力响应规律。本文首先对模型进行了试算,通过对计算结果收敛性的分析,验证了程序有限元计算的正确性和可靠性。计算分析了波流共同作用下,砂质海床瞬时振荡孔隙水压力与残余孔隙水压力累积的响应规律,获得了海床液化深度的变化特性,对比了采用弹性与弹塑性砂土本构模型时,海床在波流作用下的动态响应差异。对于不同的波流参数,包括潮流流速,波浪周期以及波浪的相对水深,进行了参数分析,得出了不同的波流荷载对海床液化的影响规律。文中对不同的海床条件对海床液化深度的影响规律进行了参数分析,包括海床厚度,海床渗透系数,海床相对密度的影响。本文研究了粉土与粘土在波流共同作用下的液化或者弱化问题,并通过对采用日本阪神地震液化土计算参数的海床液化分析,对弹塑性参数对海床液化的影响,做了简单地分析研究。通过以上的研究内容,得出基于上下负荷面剑桥模型,可以有效的模拟在波流共同作用下的砂质海床液化响应规律,包括振荡孔隙水压力响应和累计孔隙水压力响应,海床渗透系数决定了海床孔隙水压力响应差异,海床厚度,相对密度对海床液化影响较小。波浪周期越大,潮流流速越大,相对水深越小,海床液化深度也就越小。本文研究成果对我国近海海岸安全,海洋结构物建设与设计以及其安全性,提供了理论指导。更多还原

【Abstract】 In the study of marine geotechnical engineering, the seabed-structures -wave interaction has been the focus of the current research. The main factor that affects the seabed structure’s stability is the stability of the seabed foundation, so the research of the stability of the seabed is essential in this field. The seabed soil, which is mainly saturated soil and the stress environment is complex, its stability performance mainly include the surface displacement, the shear modulus of elasticity and changes in responses of excess pore water pressure and the seabed’s liquefaction. The liquefaction of the seabed will lead to a sharp decrease of the capacity of the seabed foundation. So, the seabed liquefaction is the focus of this paper. Based on the u-p dynamic theory, the dynamic FEM equations are deduced using the finite element method for the solid phase and the finite difference method for the fluid phase. Then a fully coupled dynamic FEM program can be developed, in which the stress induced anisotropic elastoplasticity constitutive model is implemented. The poro-elastoplastic model for a sandy seabed can be established to conduct the numerical simulation. Subsequently, the excess pore pressure can be obtained to compute the liquefaction depth of the seabed according to the theory of effective stress. Firstly, a confirmatory case is conducted and the program is proved to be valid and reliable by analyzing the numerical results’convergence. The mechanics of oscillatory excess pore water pressure in seabed and residual excess pore pressure due to wave/current are discussed and the liquefaction depth which changes correspondingly is obtained. A comparison between the elastic and elatoplastic sandy seabed’s dynamic responds to wave/current loading is also presented. The influence of parameters of the wave/current on the liquefaction of the seabed is also studied in this paper, including current velocity, wave period and relative water depth. This paper studies the impacts of the seabed conditions on the seabed’s liquefaction depth including seabed thickness, permeability coefficient of the seabed and the relative density of the seabed. In this paper, the silt and clay seabed response to wave/current loadings are studied to conclude that this constitutive model can simulate the silt and clay seabed dynamic responses. To study the influence of the elastic-plastic parameters on the seabed’s liquefaction depth, the Japan’s Kobe soil, which is a representative soil which experienced dramatic liquefaction during earthquake, is used. Through the above researches, we can conclude that: this constitutive model, which is based on the super/sub-loading surface and anisotropy, can effectively simulate the behavior of the seabed under wave/current loadings and the liquefaction depth is larger than the elastic seabed. The seabed’s permeability coefficient determines the response of pore water pressure, and the seabed thickness and relative density have less impact on the seabed liquefaction. The bigger the current velocity is, the longer the wave period is and the smaller the relative seawater depth is, the liquefaction depth of the seabed is smaller. The conclusions of this thesis can contribute to the design and construction of the offshore structures and the safety of the costal line as theoretical guidance.更多还原