砂土直剪试验离散元数值模拟与细观变形机理研究

基于离散元法进行砂土直剪试验模拟与剪切宏细观响应研究。采用试样分条带法研究砂土剪切过程中的变形发育情况;记录应力-位移关系,分析砂土剪切应力、应变特性与剪胀特性。通过分析接触力链、接触组构分布、配位数及滑动接触百分比等细观行为演化研究颗粒细观接触状态演变;基于局部孔隙率变化分析颗粒细观分布状态演变;采用颗粒累积转动量和速度场分析颗粒细观运动状态及剪切带发育的细观机制;对离散元软件PFC^2D进行二次开发,实现主应力的可视化。研究表明应变局部化集中于颗粒转动、接触滑动、体胀明显的剪切带内,剪切带内外颗粒不同的运动状态导致细观参量的变化,剪切带厚度为(10~15)d₅₀;力链网络、接触组构和主应力场本质上是一致的,三者主方向在剪切过程中发生了近似一致的偏转。

Exploring Mesoscopic Deformation Mechanism of Sand in Direct Shear Test by Numerical Simulation Using Discrete Element Method

Direct shear test of sand was simulated using discrete element method and the macro-and-mesoscopic responses of sand during shearing were analyzed in this research.The development of sand deformation was observed through strip partition method;and the relationship between shear stress and shear displacement was recorded to analyze the macroscopic behaviors of sand.In mesoscopic scale,the development of contact status was researched through analyzing contact force chain,contact fabric distribution,coordination number and sliding contact percentage;the evolution of granular distribution under shearing was observed through the analysis of porosity variation;the granular motion state and the mesoscopic formation mechanism of shear band were studied through observing the cumulative rotation and velocity of particles.Furthermore,principal stresses and their inclinations in specimen were visualized through secondary development of PFC2D.The study shows that strain is concentrated in the shear band in which particle rotation,contact sliding and obvious dilatancy are observed.Different motion state of particles inside and outside the shear band leads to the changes of mesoscopic parameters,and the thickness of shear band is 10-15 times of d50.Contact force chain network,contact fabric distribution and principal stress distribution are essentially consistent,and the principal direction changes consistently during shearing.