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-  2018 

基于离散元弹性边界模拟的砂土剪切行为分析
Analysis of shear behavior of sand based on elastic boundary simulation of discrete element method

Keywords: 道路工程,砂土,离散元,弹性边界,剪切带,应变局部化
road engineering
,sand,DEM,flexible boundary,shear band,strain localization

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Abstract:

采用二维离散元方法开展数值双轴试验研究砂土剪切力学行为。将室内试验中橡皮膜对砂土试样的柔性包裹效应抽象为作用在试样边界颗粒上的指定法向压力,对传统离散元数值双轴试验进行了改进。改进后的离散元双轴试验能有效模拟室内试验中砂土试样剪切破坏后的侧向不均匀变形现象,并以此开展参数研究,探明了围压、颗粒摩擦因数等参数对砂土剪切行为的影响规律,最后从细观角度得到了剪切带形成过程与相关机理。研究结果表明:砂土应变软化与剪缩现象均随围压的增加而增强,剪胀效应则随围压增加而减弱;砂土变形模量随围压增大而增大,但增幅不明显;砂土残余强度基本不受围压影响,但峰值强度受围压影响明显,砂土峰值强度和对应的轴应变均随颗粒摩擦因数增大而增大,围压和颗粒摩擦因数对试样峰值强度的贡献是有限的;剪切带两侧的砂土颗粒均沿相反方向平移,接触力链主要沿加载方向分布,表现出卸载特性;剪切带内部的砂土颗粒出现相互错动,同时绕自身形心转动角位移较大,接触力链相应发生水平向偏转,出现明显的应变局部化现象,应变局部化首先发生在试样中心,此后迅速贯穿整个试样,同时砂土试样到达峰值强度。剪切带内部砂土颗粒结构疏松,颗粒间接触减弱,颗粒配位数减小,土体孔隙率增大。
Two dimensional discrete element method (DEM) was used to carry out numerical biaxial test to study the shear behavior of sand. By abstracting the flexible wrapping effect of rubber membrane on sand samples in laboratory test as the specified normal pressure acting on boundary particles of the sample, the conventional discrete element numerical biaxial test was improved. The improved discrete element biaxial test could effectively simulate the lateral inhomogeneous deformation of sand samples after shear failure in laboratory test, and parameter studies were carried out to clarify the effect of confining pressure and particle friction coefficient on the shear behavior of sand. Moreover, the formation process and corresponding mechanism of shear band were investigated from microscopic perspectives. The results show that strain softening and shear shrinkage of sand increase with the increase of confining pressure, while the shear dilatancy decreases with the increase of confining pressure. The deformation modulus of sand increases with the increase of confining pressure, but the increase is not obvious. The residential strength of sand seems not to be affected by confining pressure, while the peak strength is obviously affected by confining pressure. The peak strength and corresponding axial strain increase with the increase of particle friction coefficient. The contribution of confining pressure and particle friction coefficient to the peak strength of the sample is limited. Soil particles on both sides of shear band move in adverse directions, and the contact force chain is distributed mainly along the loading direction, showing unloading characteristics. Soil particles within shear band are staggered, and the angular displacement is larger around its centroid, and the contact force chain deflects horizontally, resulting in obvious strain localization. The strain localization occurs at the center of the specimen initially, and then quickly through the whole specimen, and the specimen reaches the peak strength. In the shear band, the particle

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