排桩支护下颗粒介质水平拱效应研究

Study on the horizontal arching effect of particle media under pile support

排桩支护体系中水平拱效应是土体发挥自身抗剪强度所产生的一种应力重分布现象,其对工程设计和安全评价有着重要意义。水平拱效应在实际工程中是三维空间结构,但目前土拱效应研究侧重于截取三维结构中某一剖切面将其简化为平面应变问题进行分析,而忽视了拱效应的三维几何特征。将三维空间结构切成若干水平面,对不同水平面施加不同的初始应力,利用自制大尺寸光弹试验设备从二维角度分析排桩支护体系中土拱形态演化以及水平拱效应三维几何特征,并利用颗粒流PFC2D软件对模型试验结果进行重现,同时运用数值模拟手段进一步探究土拱厚度随深度的演化规律。研究结果表明:排桩在受到远场荷载作用下,其水平拱效应经历了一个发展-稳定-破坏的过程,土拱效应破坏后支挡效果显著下降;不同深度处的土拱效应存在显著差异,差异体现在桩后成拱区沿桩底方向分为未形成段、形成段、稳定发展段和破坏段,成拱区影响范围在2倍桩径范围内;成拱区厚度为成拱区上拱顶点与下拱顶点的差值,上拱顶点为沿排桩方向出现第一个σx和σy相交的点,下拱顶点为靠近排桩的σy的极大值点;成拱区厚度沿桩底方向表现为先增大后减小的趋势。

The horizontal arching effect occurs in soil supported by row piles,is caused by the stress redistribution due to soil shearing,and is of great importance for accurate evaluation of structure safety.The horizontal arching effect is practically a three-dimensional problem,while most studies simplify this fact by cutting a section of the arching with a plane strain idealization.Hereby,we cut the arching into several horizontal layers and rebuilt the vertical characteristics by applying different levels of initial stress.The evolution of the three-dimensional characteristics of horizontal arching for row-pile-braced particles was modelled with a selfdesigned large-scale photoelastic test equipment.The particle flow PFC2D software was used to model similar results and to further study the depth effect.It shows that the horizontal arching effect of particles on row piles induced by a far loading gradually became stableand finally deterred with a dramatic drop in the capacity of row piles.This effect defers with depthfor the arching area composed by four parts along the pile:the developing section,the forming section,the stable section,and the failure section.The influence range of the arching area is two times the pile diameter.The thickness,which is the difference between the upper arch vertex(the first intersection point ofσx andσy along the direction of the pile row)and the lower arch vertex(the maximum point ofσyclose to the pile row),increases initially and decreases finally along the direction of pile bottom.