密实砂土剪切过程中的颗粒运动与微观力学特征

密实砂土在剪切过程中发生剪胀,土宏观上的剪胀行为与土内部的颗粒运动及颗粒间接触力的变化特征密切相关.针对密砂剪切过程中的颗粒运动与颗粒间接触力之间的相互联系,及其对剪胀的贡献这一问题,采用离散元数值方法,模拟密实砂土分别在50 kPa和100 kPa竖向压力下直剪试验,通过对颗粒运动以及颗粒间接触力的分析,探究密实砂土...

Kinetic characterizations and micro-mechanism of dense sand subjected to shear

Dense sand dilates subjected to shearing． This macroscopic dilatancy behavior is related to soil particle motions and the variation of contact forces from the micro point of view． In order to explore the relationship and contribution to dilatancy of particle motion and contact force，in this paper，numerical simulations based on discrete element method ( DEM) are conducted to simulate dense sand in direct shear tests under 50 and 100 kPa vertical stresses，respectively． The associated changes of particle motions and contact forces are monitored to examine the kinetic characterizations，the micro-mechanisms and their relationship of dense sand subjected to shearing． In addition，the contribution of particle motion in and out of the shear band to dilatancy is also explored． The simulation results indicate that: ( 1) the sample dilatancy is controlled by the contact rolling while the contact sliding can lead to sample contraction; in the shear band，the contact rolling is larger than the contact sliding，that is，the contact rolling is dominated，hence，the dilatancy can be found; out of the shear band，the particle motion is dominated by contact sliding，which lead to the observation of sample contraction; the contact rolling decreases with increasing vertical stress，less dilatancy is observed; ( 2) the variations of main orientation and anisotropy in strong and weak forces have a good consistency with principal stress change: the main orientation of the strong forces is consistent with the principal stress direction，which is orthogonal to the main orientation of weak forces; the anisotropy of strong forces decreases while the anisotropy of weak forces increases during shearing progress，and both of them become stable at critical state; ( 3) in the shear band，the contact sliding and rolling occur in both the strong and weak force chains without selectivity; the particle motions in the shear band make the percentage of strong forces increase and the weak forces decrease，and finally become almost same; the particle motions out of the shear band reduce the percentage of strong forces and improve the percentage of weak forces，and the difference between them increases slightly．