基于离散单元法的渗流侵蚀作用下桩基位移与承载特性研究

Discrete element method based investigation on displacement and bearing characteristics of pile foundation under seepage erosion

随着城市地下空间桩基与隧道立体交叉分布体系的日渐复杂,隧道渗流侵蚀引发的桩基稳定性问题越发突出。然而,目前关于隧道破损引发渗流侵蚀方面的研究工作主要聚焦于侵蚀发生机制方面,其与邻近桩基的相互作用尚欠关注。因此,在物理试验揭示渗流侵蚀机制的基础上,通过建立土体临界细粒含量表达式,量化表征了地层侵蚀形态;随后,采用随机定量删除细颗粒的方法,基于离散单元法DEM建立了多区域侵蚀地层模型,进而分析了不同桩基位置、沉桩方式、桩基荷载和基础类型条件下桩基结构的侵蚀响应特征。结果表明,桩基受侵蚀后均产生不同程度的下沉位移,并在不平衡力的驱动下向侵蚀区倾斜;桩端阻力受损后随桩体下沉逐渐上升,侧摩阻力损失则基本无法恢复。此外,不同沉桩方式与桩基荷载下,桩体的位移与阻力变化模式基本一致,主要是变化量的不同;相比单桩,群桩具有更好的抗侵蚀能力。

With the increasing complexity of the three-dimensional cross-distribution system of pile foundations and tunnels in the urban underground space,the stability of the pile foundation caused by tunnel seepage erosion becomes more and more prominent.However,the current research mainly focuses on the mechanism of erosion induced by defective tunnels,and little on its interaction with the adjacent pile foundation.Thereby,based on the seepage erosion mechanism revealed by the physical model test,the erosion-induced stratum form is quantitatively characterized by establishing the critical fine particle content expression.Subsequently,a multi-zone eroded strata model is simulated by the random and quantitative removal of fine particles in the DEM domain,and then the erosion response characteristics of the foundation under different positions,loads,sinking methods and types are analyzed.The results show that the pile foundation has different degrees of subsidence under different erosion conditions,and tilts to the eroded area under the drive of unbalance force on its eroded position.After the erosion-induced reduction,the pile-tip resistance increases gradually with the subsidence,but the loss of lateral frictional resistance is basically unrecoverable.In addition,the changing mode of displacement and resistance of the pile is basically the same under different sinking methods and loads,only different in the changed amount.Compared with the single pile,pile group foundation has a better erosion resistance.