含可液化土层场地中浅埋地下结构地震反应模拟及破坏机理研究

Urban subway projects possibly pass through the liquefiable soil layer. The large deformation or displacement of the site caused by seismic liquefaction induce serious damage to the underground structures. In order to reveal the influence rules of liquefaction on the nonlinear seismic response and collapse mode of the underground structure, a whole analysis model of shallow underground structure in the site contained a liquefied soil layer will be constructed. A cyclic elastic-plasticity model described the large deformation during an entire liquefaction process and an artificial boundary reflected the nonlinear effect of the layered site with a liquefied soil layer are considered in the model. And an adaptive mesh scheme will be proposed to deal with the mesh distortion induced by the large ground deformation in condition of seismic liquefaction. Based on the whole analysis model and the computing method, the finite element simulation of seismic nonlinear response of shallow underground structure in the layered site with a liquefied soil layer will be studied. The influence rules of the large deformation of the site caused by seismic liquefaction, seismic oscillation and structural form on seismic response and collapse mode of underground structure will be analyzed specifically. The seismic damage mechanism and failure mode of shallow underground structure in the layered site with a liquefied soil layer will be revealed.

城市地铁工程穿越可液化土层不可避免，地震液化引起的场地大变形容易造成地下结构的严重破坏。为揭示场地液化对地下结构非线性地震反应和塌毁模式的影响规律，本项目拟采用考虑液化后大变形的砂土弹塑性循环本构模型，及考虑非线性效应的含可液化土层成层场地人工边界，拟建立一套含可液化土层场地浅埋地下结构的整体分析模型。并拟提出一种处理土体地震液化大变形引起网格畸变的网格自适应方法。基于建立的分析模型和计算方法，对含可液化土层场地浅埋地下结构的地震非线性反应进行有限元模拟，重点分析土层液化大变形、地震动、结构构造等因素对地下结构地震反应及塌毁模式的影响规律，揭示含可液化土层场地浅埋地下结构的地震破坏机理及失效模式。

地下结构的地震反应可归结为分析土与地下结构的动力相互作用问题，其数值分析方法涉及土体与结构材料的本构模型，土-结界面的动力接触问题，模型地基截取时边界的处理方法，地震动输入方法以及整体系统的有限元方程求解算法等。.针对这些关键科学问题，项目首先总结了饱和土中三种体波的传播特性，并基于此，建立了可液化土-结构动力相互作用问题的有限元整体分析模型，包括可考虑液相渗流速度的饱和土人工边界，饱和土时、空解耦的显式有限元离散方法，以及考虑液相孔隙流体贡献的条件下，可反映饱和土-结构界面“粘结、滑动和分离”接触状态的接触面模型，并在OpenSees软件中实现提出方法的计算功能。.基于已开展的局部液化夹层场地地下结构离心机振动台模型试验，以及液化场地中桩基-承台-上部结构系统的振动台试验，采用提出的有限元整体分析模型计算两个试验的动力响应。通过将计算结果与试验结果进行对比，验证了提出方法的正确性和有效性，并分析了地震作用下复杂、非线性饱和土场地的液化过程、失效模式，以及土壤液化后可能存在的场地失效或大变形对结构破坏机理与失效模式等问题提供了分析方法。数值结果定性揭示了场地的液化规律及其对结构地震反应的影响，深化了对自由场地、结构-土体系地震反应特征和规律的认识。.