基于离散-连续耦合的砂土三轴试验微细观力学行为研究

Exploring the microscale mechanism of granular soil under triaxial testing: Insights from coupled discrete-continuum approach

摘要

【目的】砂土三轴离散元模型的刚性边界难以反映试样的变形破坏。为模拟砂土及侧向约束橡胶膜的柔性变形，深入研究砂土三轴试验中颗粒尺度的微观力学特性。【方法】采用离散-连续耦合方法，基于有限差分程序FLAC^3D和离散元程序PFC^3D,使用可变形连续膜(Shell)单元和刚性离散颗粒(Ball)单元分别模拟橡胶膜与砂颗粒，建立耦合模型，获得剪切破坏过程中颗粒滚动和滑动的演变规律以及法向和切向接触力的分布特性。【结果】结果显示：耦合模型在三轴剪切过程中表现出应变软化趋势，其应力-应变曲线与真实室内试验结果相近，较好地还原了砂土室内三轴试验的变形破坏过程；加载时，试样中颗粒的平均接触数逐渐增加，微观结构趋于稳定；试样的剪切变形主要由颗粒滚动引起，而破坏软化阶段滑动颗粒数上升；压缩后，试样颗粒法向接触力各向异性显著，切向接触力分布均匀，法向接触力在承载偏应力中起主导作用。【结论】结果表明：离散-连续耦合模型能够有效模拟三轴试验中砂土的微观力学行为；模型考虑了传统耦合算法导致的试验条件偏差，通过修正离散单元以及耦合系统整体的平衡条件，解决了传统耦合算法中难以精准模拟试验条件的问题，实现了对砂土微观力学特性在颗粒尺度上更真实、准确的刻画，为深入理解砂土宏微观力学行为及相关工程应用提供了全新视角与更坚实的理论支撑。

Abstract

[Objective] The rigid boundaries of the discrete element model for sand in triaxial tests have difficulty in reflecting the deformation and failure of the specimen. To simulate the flexible deformation of sand and the lateral confining rubber membrane and conduct an in-depth study on the micro-mechanical characteristics at the particle scale in the triaxial test of sandy soil, [Methods]the discrete-continuous coupling method was adopted. Based on the finite difference program FLAC^3D and the discrete element program PFC^3D, the deformable continuous membrane(Shell) element and the rigid discrete particle(Ball) element were used to simulate the rubber membrane and sand particles respectively, and a coupling model was established to deeply investigate the evolution laws of particle rolling and sliding as well as the distribution characteristics of normal and tangential contact forces during the shear failure process. [Results] The results show that, the coupling model exhibits a strain softening trend during the triaxial shearing process, and its stress-strain curve is similar to the real laboratory test result, well reproducing the deformation and failure process of the sand in the laboratory triaxial test. During loading, the average contact number of particles in the specimen gradually increases, and the microstructure tends to be stable. The shear deformation of the specimen is mainly caused by particle rolling, while the number of sliding particles increases during the failure softening stage. After compression, the normal contact force of the specimen particles shows significant anisotropy, the tangential contact force is evenly distributed, and the normal contact force plays a dominant role in bearing the deviator stress. [Conclusion] The discrete-continuous coupling model can effectively simulate the micro-mechanical behavior of sand in triaxial tests. The model takes into account the deviation of test conditions caused by the traditional coupling algorithm and solves the problem of difficultly accurately simulating test conditions in the traditional coupling algorithm by correcting the equilibrium conditions of discrete elements and the overall coupling system, achieving a more realistic and accurate characterization of the micro-mechanical characteristics of sand at the particle scale, providing a new perspective and a more solid theoretical support for in-depth understanding of the macro and micro mechanical behaviors of sand and related engineering applications.

关键词

离散-连续耦合 / 砂土 / 三轴剪切 / 微细观特性 / 颗粒组构 / 力学性能 / 变形

Key words

discrete-continuum coupling / sand / triaxial shear / microscopic characteristics / particle structure / mechanical properties / deformation

基金资助

国家自然科学基金项目(42107192)