基于颗粒抗转动模型的刚性挡墙被动土压力临界状态离散元分析

A distinct element analysis of critical state passive earth pressure against a rigid wall using a rolling resistance contact model

简要介绍了颗粒抗转动模型,并将其引入离散元程序中,通过建立挡墙地基模型和合理选取模型参数,分别考虑了地基填土不同密实度和挡墙不同位移模式(被动T模式、RB模式、RT模式)情况下,刚性挡墙被动土压力随挡墙位移增长发展到达临界状态时,土压力系数hk随位移发展的变化规律及墙后填土剪切带的形成规律,并与其他学者的研究成果进行对比分析。研究结果表明,土压力系数hk随着挡墙位移增长的变化规律与填土的孔隙比(或相对密实度)和挡墙的位移模式紧密相关。随着孔隙比的减小或相对密实度的增大,土压力系数hk会逐渐由位移硬化特性过渡为位移软化特性。尽管中密试样在双轴压缩试验中呈现出应变软化特性,而中密样的土压力系数hk随着挡墙平动位移的增长可能呈现出位移软化特性,也可能呈现位移硬化特性。随着刚性挡墙向墙后土体推移,试样中的剪应变随之增大,并会在墙后形成应变局部化,即剪切带的出现。与室内试验剪应变云图相似,离散元较好地模拟了土压力临界状态时剪切带分布规律。同时,墙后土体表面不再是光滑的平面,而是逐渐隆起的凹凸面;随着挡墙位移增长,土体表面隆起量越来越大,直至土体破坏。

A contact model considering rolling resistance is introduced and implemented into the distinct element method （DEM） for analyzing the earth pressure at critical state against a rigid wall. The variation of earth pressure coefficient kh and the shear band formation in the backfill material are analyzed, when the passive earth pressure varies with displacement for the retaining wall with different densities and different displacement modes （passive T mode, RB mode, RT mode）. The DEM simulation results are compared with those of other researches. It is shown that earth pressure coefficient kh is greatly affected by different void ratios and wall displacement modes. The kh -displacement relation switches from hardening to softening when the void ratio decreases or the relative density increases. In contrast, the kh -displacement relation demonstrates either hardening or softening feature for the medium dense backfills even they exhibit a strain softening response in the biaxial compression tests. As the retaining wall moves to soil behind the wall, the shear strain increases and the strain localization occurs, i.e. shear band forms in the soil behind the wall. Similar to the shear strain field from laboratory experiment, the distributions of the shear band in the critical state are better simulated by DEM. Meanwhile, the surface of the backfill is no long a smooth surface rather than an upheaval surface, the value of upheaval increases significantly with the increase of the displacements of retaining wall, and finally the soil body behind the wall damages.