密实砂土剪切过程中的微观结构响应

Microstructural response during shearing process of dense sand

砂土的结构性是影响砂土力学行为的重要因素。在考虑了颗粒间的滚动摩擦的离散元方法进行双轴压缩试验数值模拟的基础上,深入分析颗粒排列、颗粒间接触方向、接触力、孔隙等的微观结构变化对于砂土剪胀的影响,以及各组分微观结构变化之间的联系,从而较全面地揭示砂土剪胀过程的微观结构响应。结果表明:(1)考虑了滚动摩擦的数值模拟结果在宏观力学响应上与真实试验更加吻合。(2)试样剪切强度主要由法向力贡献,并受强力链上接触法向的各向异性控制,弱力链对试样剪切强度贡献较小。(3)孔隙的各向异性程度与应力应变曲线具有很好的一致性,并都趋向于朝垂直方向排列;大孔隙各向异性及形状变化幅度相对较小,但其对试样体应变的贡献大,对剪切强度贡献小;小孔隙各向异性的变化幅度大、形状改变也较大,但对变形贡献较小,对剪切强度贡献大。(4)孔隙的各向异性、形状与接触法向各向异性的变化有着密切联系,即,颗粒接触法向的各向异性增加使得其对应主方向的孔隙周围的接触法向朝主方向集中,孔隙变小、形状变得更扁平,从而提高试样剪切强度并使试样剪缩,反之则使孔隙周围的接触法向偏离主方向,孔隙变大,从而减小试样剪切强度并使试样剪胀。

On the basis of the numerical simulation of biaxial compression test made with the discrete element method with the consideration of rolling friction among particles,the influences from the changes of the microstructures of particle arrangement,contact direction among particles,contact force,pore,etc.on the shear-dilation of sand as well as the relationship among the microstructural changes of all the components are deeply analyzed herein,and then the microstructural response during the shear-dilation process of sand is more comprehensively revealed.It is concluded that(1)the numerical simulation result with the consideration of rolling friction is more coincided with that from the true test on the aspect of macromechanical response.(2)the shearing strength of the test sample is mainly contributed by the normal force and dominated by the contact normal anisotropy on strong-force chain,while the contribution from the weak-force chain on the shearing strength of the test sample is less.(3)the anisotropy degrees of pores are better consistent with the stress-strain curve and all tend to be vertically arranged,while the anisotropy and shape changing amplitude of macro-pore are smaller,but its contribution is larger to the strain of test sample and smaller to the shearing strength.The changing amplitude of the anisotropy of small pore is large with large shape change,but its contribution is smaller to the deformation and large to the shearing strength.(4)the anisotropy and shape of the pore are closely related to the change of contact normal anisotropy,namely,the increase of the anisotropy in the normal direction of particle contact makes the contact normal direction around the pore corresponding to its main direction be concentrated to the main direction,while the pore becomes smaller and the shape becomes more flat,thus increases the shearing strength of the test sample and causes the shear-shrinkage of the test sample,otherwise,makes the normal contact direction around the pore deviates from the main direction with the enlargement of pore,and then decreases the shearing strength of the test sample and causes the shear-dilation of the test sample.