可液化地基中群桩基础地震响应机理的数值仿真研究

China’s rapid infrastructure development has seen significant increase in the construction and application of pile foundations, especially in areas of high seismic risk, thus generating new demands and challenges for the seismic design of pile foundations. This project focuses on studying the seismic response patterns and mechanisms of pile groups in liquefiable grounds, and aims to enhance the understanding of its seismic behaviour. Systematic numerical simulations will be conducted to reproduce the seismic behaviour of pile groups in liquefiable ground, based on validations from existing physical test data. High-performance numerical simulation methods will be established for pile groups in liquefiable ground, and a micromechanics based constitutive model for the large post-liquefaction deformation of sand will be developed. The seismic response pattern obtained from systematic numerical simulations will be summarized to analyse the influence of key aspects of the soil-pile-structure system on the seismic behaviour of pile groups. The mechanisms for the time and spatial distribution of forces and deformation on pile groups will be explained, with focus on the kinematic and inertial interaction coupling mechanism during the entire seismic event, and the distribution of forces and deformation within the pile group. This project is expected to offer new perspectives and methods for the seismic design of pile groups in liquefiable ground.

我国基础设施建设中大规模应用桩基础，对桩基础的抗震研究提出了新的需求与挑战。本项目以可液化地基中群桩基础为研究对象，以高性能数值仿真为研究手段，以已有相关试验成果为研究基础和验证依据，开展系统的大规模数值试验，再现震动响应现象和规律，核心目标在于揭示其震动响应机理。首先，在支撑理论和技术层面，利用离散元方法和弹塑性本构框架，发展砂土液化数值模拟所需的基于细观机理的砂土液化大变形本构模型，并利用大规模并行计算方法，开发可液化地基中群桩基础数值模拟所需的高性能数值仿技术；其次，在关键现象和规律层面，通过系统的数值试验，总结可液化地基中群桩基础的震动现象和规律；从而最终在核心机理和理论层面，利用动力学和统计分析手段，揭示地震作用下可液化地基中群桩基础的受力变形时间和空间分布机理。本项目预期将为可液化地基中群桩桩基础的抗震分析与评价提供新思路与新方法。

项目针对我国基础设施建设中大规模应用桩基础带来的抗震需求，开展了可液化地基中群桩基础的动力响应分析方法与机理研究。紧密结合可液化地基中群桩基础数值仿真中对砂土本构模型的需求，发展基于细观机理的砂土液化大变形本构模型。其中，揭示了砂土液化变形细观组构机理，揭示了砂土在三维应力主轴旋转条件下变形规律和细观物理机制，建立了细观组构演化与砂土各向异性的定量关系，建立考虑细观组构演化及各向异性的砂土液化大变形本构模型。利用分布式内存并行框架，在GEOS高性能数值仿真平台上开发了针对岩土工程非线性特点的基于MPI的分布式内存高效并行算法，在平台中实现了高效高精度的流固耦合动力固结算法，并对基于细观机理的砂土液化本构模型提出具体的高效数值积分方法，发展可液化地基中群桩基础高性能三维动力仿真方法。为了实现大规模数值仿真结果动态交互式可视化，开发了多平台软件GIV。采用所开发本构模型和高性能计算方法，对液化地基中散体群桩动力响应进行了深入研究，揭示了散体桩不同刚度、排水和加密效应下加固可液化场地的动力响应规律，揭示了不同置换率、不同长细比、不同土体渗透系数、倾斜场地、含低渗透夹层场地等工况的动力响应规律，以及散体桩加固可液化场地的群桩效应等动力特性。