松散砂土扩散性失稳破坏机理与大变形流滑灾变SPH数值模拟

Diffuse instability usually occurs in saturated loose sand and induces flow type disasters with large deformation. Hence, it is necessary to accurately predict such diffuse instability and flow failure. To better understanding the mechanism of diffuse instability, this project first performed laboratory experiments using hollow cylinder apparatus and ring shear apparatus to investigate the diffuse instability phenomenon under non-proportional loading. Then, the three dimensional non-coaxial micromechanics-based constitutive model, which is based on kinematic-hardening law, is used to study the mechanism of diffuse instability under non-proportional loading with the Hill's second-order work criterion in predicting the diffuse instability. An implicit integration scheme for the non-coaxial micromechanical-based constitutive model is then proposed in this study. Finally,the proposed non-coaxial micromechanical-based contitutive model and a Bingham fluid model are inplemented in the smoothed particle hydrodynamics (SPH) method, which is pure Lagrangian and meshless. The numerical method is applied to analyze the diffuse instability of saturated loose sand and the succeeding flow failure with large deformations. Case studies are also carried out to verify the applicability of the SPH method. This study is aim to provide theorietical tools for assessing the geoenvironmental disasters induced by soil instability.

饱和松散砂土往往会发生扩散性失稳，进而会发展成为大变形流滑灾变，因而合理预测这种扩散性失稳破坏及其大变形流滑过程是十分必要的。本研究针对当前饱和松散砂土扩散性失稳破坏机理与大变形流滑灾变数值模拟方法研究所存在的不足，通过可独立四维应力空间加载的空心圆柱剪切试验以及环剪试验，探讨非比例加载条件下饱和松砂扩散性失稳现象；采用基于运动硬化准则的砂土三维非共轴微宏观本构模型和Hill二价功判别准则，分析非比例加载条件下松砂的扩散性失稳破坏机理；提出砂土非共轴微宏观本构模型的隐式积分计算方法；基于砂土微宏观本构模型及流态化本构模型，结合纯拉格朗日无网格的光滑质点流体动力学（SPH）方法，形成一种真正能够分析饱和松散砂土扩散性失稳破坏以及大变形失稳流滑灾害过程模拟的数值分析方法，并应用于历史记录的实例分析验证，为预测土体失稳带来的环境土工灾害评估提供理论依据。

扩散性失稳(静态液化)是饱和砂土在不排水加载条件下出现的一种破坏模式。由于砂土孔隙中的超孔隙水压削弱了颗粒间的相互作用力，使得砂土发生失稳时的强度值大大低于砂土在排水条件下的强度值。饱和砂土的这种失稳特性与坡角比较低的海滩边坡和海底人工堆积砂土边坡的稳定性息息相关，而对于该失稳过程的力学机制尚缺乏全面的了解。本项目从本构理论的角度研究了饱和砂土扩散失稳的破坏机理，并采用离散元方法进行了验证，还建立了分析扩散性失稳破坏大变形的数值分析方法。取得主要的研究成果有：(a)基于材料失稳二阶功准则，建立了饱和土体静态液化失稳理论判别准则。分析了加载方式、K0固结条件、土体各向异性以及非饱和状态对静态液化触发的影响；（b）采用离散元方法模拟了砂土K0固结试验、饱和砂土三轴排水和不排水试验以及空心圆柱排水剪切试验，获得了宏观本构模拟相近的结果，总结了砂土失稳时的相关微观特征；（c）提出一种考虑砂土微观组构特征的各向异性和非共轴特性的本构模型，成功模拟了空心圆柱剪切试验中砂土的非共轴变形特性；（d）推导了状态相关本构模型的半隐式和隐式积分格式，建立了考虑不排水条件的失稳破坏大变形有限元分析方法，并在ABAQUS软件平台中通过二次开发进行数值实现，通过算例分析验证了方法的有效性。本项目研究成果可为预测评估失稳诱发的土工环境灾害提供理论依据。