粗粒土二维模型试验的组构分析

粗粒土的组构主要指土颗粒的几何排列方式,是决定粗粒土宏观力学性质的根本因素。为研究组构对粗粒土应力应变关系的影响,进行了粗粒土二维模型试验研究。应用计算机图像测量分析系统对模型试验图片进行分析,能定量地分析试验过程中颗粒的位移、转角、长轴的定向、配位数及枝向量的变化。图像处理结果表明,模型试验过程中颗粒的运动规律与三轴试验过程中颗粒的运动规律一致,说明模型试验能反映三轴试验过程。颗粒位移矢量图和颗粒错动矢量图分析说明,宏观应变均由颗粒调整得到,在变形的不同阶段均有颗粒错动发生,随着变形的发展发生错动的颗粒数量增多,并逐渐集中到剪切带上。颗粒长轴和枝向量的定向性与偏应力有很好的关系,定向性增强应力是增长的;反之,定向性减弱应力是衰减的。对于接触紧密的颗粒,随着变形的发展平均枝长的变化不是很明显。平均配位数与体变之间没有很好的关系,可能与模型试验中采用多边形颗粒及颗粒偏大有关。

Fabric analysis of two-dimensional tests for coarse-grained soils

The fabric of coarse-grained soils primarily refers to the arrangement of soil particles,and it is the kernel factor for mechanical properties of coarse-grained soils.Two-dimensional tests were conducted in order to study the influence of fabric on stress-strain relationship of coarse-grained soils.The model test images are analyzed by a computer image measuring system,and the particle displacement,rotational angle,long axis orientation,coordination number and branch vector are analyzed quantitatively through the system.The calculated results show the particle movement of two-dimensional tests has the same law as that of triaxial tests,which means the model tests can reflect the process of triaxial tests.The vector graphs of particle displacement and particle dislocation indicate that the macro-strain originates from particle adjustment,particle dislocation occurs at different deformation stages,the number of particle dislocation increases with deformation development,and finally the particle dislocation concentrates on shear band.The orientation of particle long axis and branch vector have good relationship with the deviator stress,and the stress increases with orientation enhancement,and the stress attenuates with orientation decrease.The change of the average branch length is unnoticeable with deformation development for intimately contacted particles.The average coordination number is not in good agreement with the volumetric strain,which is probably related to polygon particles and large particles.