Constitutive modeling of post-liquefaction cyclic response of sands

液化后的大变形是引起地基和土工结构地震灾害的主要原因，在几次有充分记录的地震中观测到液化后的大变形已成为广泛研究的课题。虽然颗粒材料的本构建模已经取得了进展，特别是在临界状态土力学平台上和使用边界面塑性，但在液化后状态下的剪切应变建模仍然存在重大挑战。该项目的目标是扩展SANISAND系列模型的制定。尽管SANISAND在液化开始点（接近零平均有效应力）之前的数学公式很优雅，但在低平均约束压力下预测的剪切应变积累与实验室实验不一致，并且在液化后状态下的模型预测与实验中观察到的结果有显著差异。所涉及的机制的复杂性，以及对所涉及组件（如微机械结构和刚度）测量的实验限制，证明了根据物理假设使用数学和计算工具（如离散元素建模（DEM））来理解所涉及的机制。研究计划有四个明确的部分。第一部分是利用DEM模拟从粒子到粒子的角度研究问题的本质。第二部分涉及SANISAND模型公式的扩展，其中模型扩展将从DEM仿真结果中获得灵感，并将其纳入基于二维和三维连续体的有限差分平台的现有模型实现中。在第三阶段，最终开发和实现的本构模型将被验证和验证，以确保其性能和鲁棒性，因此编译后的模型可以作为动态链接库（DLL）供该领域的其他建模者访问。最后，开发的工具将用于模拟地震事件中尾矿坝基础的液化反应。****

Large post-liquefaction deformation is a major cause for seismic induced hazards in soil foundation and geotechnical structures, and has been a subject of extensive research since its observations in several well documented earthquakes. While there has been advances in constitutive modeling of granular materials, particularly within the platform of critical state soil mechanics and with the use of bounding surface plasticity, significant challenge is still remaining in modeling the shear strains in the post-liquefaction regime. The objective of this project is to extend the formulation of the SANISAND family of models. Despite of the elegant mathematical formulation of the SANISAND up to the point of initiation of liquefaction (nearly zero mean effective stress), the predicted shear strain accumulation at low mean confinement pressure is not in agreement with laboratory experiments, and the model predictions in the post-liquefaction regime significantly differ from those observed in the experiments. The complexity of the mechanisms involved, and experimental limitations on measurement of the involving components such as micro-mechanical fabric and stiffness, justify the use of mathematical and computational tools in accordance with physical postulates, such as discrete element modeling (DEM), for understanding the involved mechanisms. The research proposal has 4 well-defined parts. The first part is to study the nature of the problem from a particle-to-particle perspective using DEM simulations. The second part deals with the extension of the formulation of SANISAND model, where the model extension will be inspired from the DEM simulation results, and incorporated to an existing model implementation in 2- and 3-dimensional continuum based finite difference platform. In the third phase the resulting developed and implemented constitutive model will be verified and validated, to ensure about its performance and robustness, so the compiled model can be made accessible as a Dynamic Linked Library (DLL) to other modelers in the field. Finally, the developed tool will be used in modeling the liquefaction response in the foundation of a tailings dam during a seismic event.****