砂土液化大变形模型在FLAC^(3D)中的开发与应用

Implementation of a plasticity model for large post-liquefaction deformation of sand in FLAC^(3D)

通过FLAC^(3D)二次开发平台,在VC++环境下实现了基于砂土液化大变形机制的变动映射中心边界面弹塑性模型的二次开发。基于饱和砂土液化大变形本构理论,该模型符合三维应力空间边界面映射规则,并引入临界状态变量,可实现对不同密度和围压状态下砂土液化大变形分析。针对FLAC^(3D)程序混合离散技术与数据调用模式和模型的体积相容性条件,测试分析了将模型采用不同植入方案的计算稳定性,开发了在FLAC^(3D)混合离散技术下不同子区共享映射中心,进入与离开液化状态保持同步的开发方案,并给出模型开发的关键技术与实施方法。利用开发的模型,对饱和砂土开展了不排水/排水/循环三轴试验与不排水循环扭剪试验模拟,及三维地基的动力反应分析。计算结果表明,模型及所开发程序具有很好的模拟与分析砂土液化后大变形的能力。

The purpose of the study is to improve the simulation of liquefaction of sands and variations in effective stress when using FLAC^3D for the dynamic analysis of liquefiable ground and structures. Based on the physics of large post-liquefaction deformation of sand, a bounding surface plasticity model with appropriate mapping rules for plasticity and dilatancy in three-dimensional stress space is developed. A state parameter for compatibility with critical state soil mechanics enables the simulation of sand at various densities and confining pressures with a same set of parameters. According to requirements and procedures of user-defined-model（UDM）, the plasticity model is successfully implemented into FLAC^3D code in Visual C＋＋ environment. After testing the calculation stability, the implemented schematics allow subzones of the mixed discretization process in FLAC^3D share mapping center and simultaneously enter and leave liquefaction status. Using the program, undrained and drained triaxial tests, cyclic triaxial tests, undrained cyclic torsional tests are simulated and a three-dimensional site dynamic response analysis is also performed. The results show that the model and the implemented program have superior and reasonable capability to simulate small and large deformation in pre-to post-liquefaction phase of sand.