孔压触变性流体中的桩基地震破坏机制和分析方法

To analyze and evaluate the seismic resistance of pile foundations in liquefiable sites is a difficult problem. The particle discrete element method will be employed to simulate the evolution process of mesoscopic soil particle contact state and macroscopic dynamic response. The liquidity generation mechanism of the liquefiable soil will be revealed. Combining with the large diameter dynamic triaxial tests, the fluidity evaluation method and its evolution law will be studied. The theoretical basis and methods to determining the conditions of phase change of liquefiable soils will be proposed. And the hypothesis that the liquidity is induced by thixotropy effects from the pore water pressure is expected to be verified. Subsequently, the rate equation and state equation of the pore water pressure induced thixotropic fluid will be studied. The structure state parameter will be expressed using the liquidity index. The constitutive model of the pore water pressure induced thixotropic fluid will be built and some parameter sensitivity analysis will be conducted. The tests of dragging tube in liquefied soils are developed using shaking table and the rate-dependent lateral pressure is discussed. The simplified seismic analysis method of pile foundation in the pore water pressure induced thixotropic fluid under the non-liquation soil layer will be proposed. The dynamic fluid level problem of the viscous liquid under the non-liquation soil layer will be discussed. To consider the phase change process of the liquefiable soils, a staged calculation mode will be studied. A numerical simulation technology for the fluid-solid full coupling seismic analysis of the pile foundation in the pore water pressure induced thixotropic fluid under the non-liquation soil layer will be developed. The above mentioned two methods will be examined through the simulation of the real earthquake-induced damage examples. The design cases with different initial value and boundary value conditions will be comparatively analyzed using shaking table test and numerical simulation. According to the staged characteristics of seismic responses of pile foundation in the liquefiable sites, the rate-dependent pile-soil interaction and its effects will be revealed. The causal relationship between the liquefaction effect and pile foundation earthquake damage also will be discussed. It is explained that the failure mechanism of pile foundation in liquefiable sites.

可液化场地桩基抗震性能分析和评价是一个难点问题。应用颗粒离散元模拟细观土颗粒接触状态和宏观动力响应的演变过程，揭示土体流动性产生机制。结合动三轴试验，研究流动性评价方法及其演变规律，提出确定土体相变条件的理论方法，证实孔压触变流动性。研究以流动性指标表征土体结构状态参数的流体速率方程和状态方程，建立孔压触变性流体本构模型并进行参数分析；开展液化土中管体牵引试验，研究侧向压力率相关性，提出非液化层覆盖的孔压触变性流体中桩基地震反应简化分析方法；研究非液化层覆盖下粘性流动态液面模型和考虑土体相变过程的分段计算模式，开发孔压触变性流体中的桩基地震反应流-固耦合数值试验技术，模拟震害实例验证上述方法；对不同初边值条件的设计案例开展振动台试验和数值模拟对比分析，获得桩基地震反应阶段性特征，揭示桩-土率相关相互作用效应及其影响，评价液化效应与桩基地震破坏关系，科学解释可液化场地桩基地震破坏机制。

本项目将可液化土体视为流体，围绕可液化场地桩基抗震性能分析和评价问题开展了深入研究。首先，应用颗粒离散元模拟细观土颗粒接触状态和宏观动力响应的演变过程，揭示了土体流动性产生的细观机制，提出了以界限力链强度判断土体流动性产生的标准；利用不排水循环三轴试验，研究了流动性评价方法及其演变规律，发现可液化土体的孔压触变性，并从流体角度解释了循环活动性；提出了描述循环荷载下土体液化过程的统一触变模型，建立了基于流体触变理论的振动孔压增长模型，并应用于土体的液化判别。开展了液化土中管体牵引试验，提出了桩-可液化土率相关相互作用的概念，建立了桩-可液化土率相关相互作用拟静力简化分析方法；开发了孔压触变性流体中的桩基地震反应流-固耦合数值试验技术，分析了时变和时不变可液化场地桩基地震反应特征，明确了上覆非液化层及厚度对桩基阶段性地震反应的影响；开展了多种初边值条件下的可液化场地桩基振动台模型试验，揭示了液化场地的流动效应，获得了可液化场地桩基地震反应的阶段性特征，科学解释了可液化场地桩基地震破坏机制。