Constitutive modeling of post-liquefaction cyclic response of sands

液化后大变形是引起地基和岩土工程结构地震灾害的主要原因之一，自几次有据可查的地震中观测到液化后大变形以来，液化后大变形已成为广泛研究的课题。虽然在粒状材料的本构建模方面取得了进展，特别是在临界状态土力学的平台内，并使用边界面塑性，但在液化后状态下的剪切应变建模方面仍然存在重大挑战。该项目的目标是扩大SANISAND系列模型的制定。尽管优雅的数学公式的SANISAND开始液化点（近零平均有效应力），预测的剪切应变积累在低平均围压是不符合实验室实验，在液化后制度的模型预测显着不同于那些在实验中观察到的。所涉及的机制的复杂性，和实验的限制，测量的涉及组件，如微机械织物和刚度，证明使用数学和计算工具，根据物理假设，如离散元建模（DEM），了解所涉及的机制。该研究计划有四个明确的部分。第一部分是从粒子到粒子的角度使用DEM模拟来研究问题的本质。第二部分涉及SANISAND模型公式的扩展，其中模型扩展将从DEM模拟结果中得到启发，并将其结合到基于二维和三维连续体的有限差分平台中的现有模型实现中。在第三阶段，将对所开发和实施的本构模型进行验证和确认，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人员访问。最后，开发的工具将用于模拟地震事件期间尾矿坝地基的液化反应。*

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.****