界面不规则多层场地砂土地震液化研究

Most cities in China are located in plains, and the stratum structures usually have irregular surfaces, which have significant influence on the initial stress state of the soil, the drainage condition and dynamic load during earthquake. However, due to the complexity of the stratum structure, this influence is not considered in the current method for the hazard assessment of sand liquefaction. This project aims to reveal the influence mechanism of layered ground with irregular surfaces on the sand liquefaction through the numerical simulation and high gravity centrifuge model test. First, based on the Biot theory, the solution for the dynamic response of a typical saturated multi-layered soil with irregular interfaces are given. Using this solution, the dynamic stress paths in a multi-layered soil with typical stratum structure are studied. Second, through laboratory tests, the dynamic behavior of sand with different initial stress states and typical dynamic stress paths is studied. The numerical simulation technique and high gravity centrifuge model test are used to reproduce the space-time evolutionary process of the sand liquefaction in multi-layered soil. We try to reveal the influence mechanism of the stratum structure on the sand liquefaction and establish the relationship between the stratum structure and the failure mode of the ground. Finally, the method for hazard assessment of sand liquefaction and the corresponding ground treatment are proposed are proposed.

我国大部分城市位于平原地区，场地一般为界面不规则的多层土体。地层结构形式对砂土初始应力状态、排水条件以及地震中动荷载形式等均有重要影响。然而，由于地层结构形式复杂多变，现行的地基液化危害性评价体系中并没有考虑这一影响因素。本项目拟通过超重力离心机试验和数值模拟，揭示界面不规则地层结构对场地砂土层液化的影响机制。首先，基于Biot饱和多孔介质理论，研究界面不规则多层饱和多孔介质稳态响应，分析典型界面不规则多层场地中土单元体动应力路径。其次，通过室内单元体试验，研究具有不同初始应力状态的砂土在典型动应力路径作用下的动力特性。开展超重力离心模型试验和数值模拟，再现场地砂土层液化触发及时空演化全过程，揭示界面不规则地层结构对场地砂土层液化的影响机制，明确地层结构形式与场地破坏模式间关系。最终，提出实用的场地液化危害评价方法及工程处置对策。

从全球来看，近期地震活动性有加强趋势。因此急需加强岩土地震工程领域中的关键力学问题研究，形成对国家需求的重要支撑能力。地震过程中，场地地层结构形式对场地内不同位置处砂土动力响应具有重要影响。本项目开展了具有弱渗透性覆盖层的砂土场地地震液化的超重力离心机模型试验，再现了多层场地内砂土层液化发生和发展全过程，研究了地层结构和动载荷强度对砂土层内部首先发生局部液化区域及其时空演化规律的影响机制，揭示了地层结构与场地破坏模式间的关系。基于弹性介质理论，将地震荷载假设为轴对称荷载，分别研究了P波和S波震源作用下半无限场地内不同位置处土单元体动力响应过程，给出了相应的解析解，并编制了计算程序。基于Fredlund和Hasan提出的非饱和土理论，研究了动荷载作用下孔隙水和孔隙气在多层土体内的运移规律，并分析了孔隙率、饱和度、渗透系数以及不同土层间排列方式对孔隙水压力和孔隙气压力消散过程的影响。基于Biot和Zienkiewicz提出的多孔介质理论，并将Kelvin-Voigt模型引入土骨架中，得到了粘弹性土体模型的控制方程。运用正弦和余弦变换等理论计算方法，给出了单层粘弹性土体瞬态响应问题的解析解，分析了粘弹性系数、动力渗透系数等参数对饱和与非饱和土体的动力特性的影响。