考虑颗粒形态效应的砂土动力学细观研究及地震响应多尺度模拟

Sand dynamics is complex but has a profound impact on practical geotechnical engineering. It is relevant to the operation and performance of key infrastructures in civil and mining engineering. Understanding of sand dynamics helps us build and maintain safe geostructures, and mitigate geohazards due to dynamic loadings, such as those induced by earthquakes, traffics, and waves. A key step towards the understanding and application of sand dynamics is the development of an accurate and usable soil constitutive model that accounts for various dynamic loading paths, which, however, faces many challenges. The difficulty is mainly attributable to the fact that the constitutive model based on the assumption of continuum has neglected the discreteness of sand, and its microstructure has not been fully respected in the macroscopic model. This project, therefore, starts from the micromechanics of sand by using the discrete element method simulations to investigate sand dynamics under various dynamic loading paths. The influence of particle shape on the properties of sand dynamics has been emphasized. The study aims to provide microscopic physical mechanisms for the understanding of sand dynamics and to develop sand constitutive models with fewer phenomenological parameters...Taking advantage of the multiscale character of sand, the project further develops the coupled discrete element and finite element methods for the multiscale analysis of seismic ground responses, and the failure of earthen embankment due to liquefaction under seismic loading. The new framework features a thorough consideration of realistic morphology of sand grains in the micrcoscopic representative volume element and incorporates a fully coupled hydro-mechanical formulation at the macroscopic level. This approach successfully bridges the micromechanics and macroscopic behaviors of sand, and has been proved of both scientific and practical significance.

砂土动力学特性十分复杂，在地震、交通、波浪等动荷载作用下，砂土易发生灾变导致建（构）筑物失稳破坏，深入研究砂土的动力学特性具有重要的工程意义。建立准确适用并能描述复杂应力路径下砂土动力特性的本构模型面临诸多挑战，主要原因在于基于连续介质假设的传统本构模型忽视砂土的离散特性，其细观结构在宏观模型中未能得到充分反映。本项目拟从砂土细观力学机制出发，揭示砂土在复杂动应力路径下的力学响应，研究砂土颗粒形态对动力学特性的影响，为动力本构模型的建立提供细观物理机制，以减少模型中的唯象假设。本项目进一步采用离散元与有限元耦合的多尺度分析方法模拟砂土场地地震响应，以及堤坝等土工结构物的液化破坏过程，实现砂土材料力学行为从细观到宏观的跨尺度表征，预期研究成果具有重要的科学理论价值和工程应用价值。

砂土动力学特性十分复杂，在地震、交通、波浪等动荷载作用下，易发生灾变致建（构）筑物失稳破坏。同时砂土由离散颗粒构成，具有鲜明的多尺度特征，宏观力学行为受微观结构支配。本项目在理论分析层面，通过考虑真实砂土颗粒不规则形态的离散元模拟及应力分量伺服控制技术，揭示了砂土在复杂动应力路径下的微观力学响应机制，阐释了颗粒形态对砂土抗剪强度及临界状态的影响规律，支持和完善了砂土的各向异性临界状态理论。在模型方法层面：一是建立了耦合有限元与离散元的分阶多尺度模拟方法，结合了两种方法各自的优势，开发了该方法的大规模并行计算程序，其中离散元模型可考虑颗粒的复杂形状，使用该方法分析了各向异性砂土上浅基础的承载力特征和非对称破坏模式；二是开发了岩土工程大变形问题模拟的光滑粒子有限元计算程序，该方法集合了光滑有限元与粒子有限元的优点，可用于研究地震诱发砂土液化致滑坡、泥石流等大变形问题；三是在耦合有限元与离散元多尺度模拟框架下，采用u-p形式求解饱和砂土的流固耦合问题，分析了间断级配饱和砂土边坡在渗流作用下的潜蚀和失稳问题。项目取得的主要学术成果：发表论文10篇（含2篇在投），其中第一或通讯作者论文6篇；做国内外特邀报告2次；发布开源计算程序1套；指导学生获第五届全国颗粒材料计算力学会议优秀学生论文奖。

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