颗粒长轴比对粗粒土抗剪强度影响的细观机理

Meso-mechanism of the effect of particle aspect ratio on shear strength of coarse-grain soil

长轴比是表征粗粒土颗粒形状的重要指标之一,研究长轴比在剪切过程中的影响和作用,对粗粒土抗剪强度特征的精确描述具有一定理论意义。以可视化直剪试验和数值分析为手段,研究剪切过程中剪切带内颗粒长轴旋转角度、剪切带宽度、空间位置差Δ和配位数等组构要素变化特征,并从细观尺度揭示不同颗粒长轴比粗粒土强度发挥过程中力链网络存在的差异性。研究结果表明:剪切过程中剪切带形成的空间分布位置存在差异性,颗粒长轴比Se越大,剪切带的空间位置差Δ越小;剪切带内颗粒长轴平均旋转量较大,向两侧逐渐减小,同时长轴比Se越大,颗粒长轴平均旋转量越小;Se影响着剪切带内强力链的密度和形态,Se越大的颗粒间接触越密集,颗粒间空隙越小,剪切带内强力链密度越大,力的传递性越好,稳定性越强,在外力作用下断裂重组后形成更稳定的结构。

The particle aspect ratio is one of the important indexes to characterize the shape of coarsegrain soil particles.Studying the influence and function of aspect ratio on the shear process of coarsegrain soil is of theoretical significance to the accurate description of shear strength characteristics of coarse-grain soil.In this paper,the variation characteristics of aspect rotation angle,shear band width,spatial position difference(Δ)and coordination number of particles in shear zone were studied by means of visual direct shear test and numerical analysis.The difference of force chain network in the process of strength development of coarse-grain soil with different particle aspect ratio(Se)was revealed at the meso-scale.The results showed that the spatial distribution position of the shear band was different during the shear process,and the larger Sewas,the smallerΔwas.The average rotation of long axis of particles in shear zone was larger and decreased gradually on both sides.In addtion,the larger Sewas,the smaller the average rotation of long axis of particles was.It indicates that Seaffects the density and morphology of strong chain in shear zone.The larger Seis,the denser the contact between particles is,the smaller the gap between particles is,the higher the density of strength chain in shear band is,the better the transmission of force is,the stronger the stability is,and therefore the more stable the structure is,which formed after fracture recombination under the action of external force.