Constitutive modeling of post-liquefaction cyclic response of sands

液化后的大变形是引起土基和岩土结构震害的主要原因，自从在几次有充分记录的地震中观察到以来，液化后大变形一直是一个广泛研究的主题。虽然颗粒材料的本构模型已经取得了进展，特别是在临界状态土力学的平台上，以及结合边界面塑性的使用，但在液化后区域的剪切应变建模方面仍然存在重大挑战。该项目的目标是扩展SANISAND系列模型的公式。尽管SANISAND在液化启动点(几乎为零的平均有效应力)的数学表达式很好，但预测的低平均围压下的剪切应变累积与实验结果不符，液化后阶段的模型预测与实验结果有很大差异。所涉及的机构的复杂性，以及对所涉及的部件(如微机械结构和刚度)的测量的实验限制，证明有理由根据物理假设使用数学和计算工具，如离散元建模(DEM)，以了解所涉及的机构。研究方案有4个明确的部分。第一部分是使用DEM模拟从粒子到粒子的角度来研究问题的本质。第二部分是SANISAND模型的扩展，该模型的扩展将受到DEM模拟结果的启发，并与现有的基于二维和三维连续介质的有限差分平台的模型实现相结合。在第三阶段，将对所开发和实施的本构模型进行验证和验证，以确保其性能和稳健性，从而使编译后的模型可以作为动态链接库(DLL)供现场其他建模者访问。最后，将所开发的工具用于模拟某尾矿库地基在地震作用下的液化响应。

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.