沉井下沉过程刃脚的极限土阻力分析

Analysis of limiting soil resistance beneath cutting curb during sinking of open caisson

考虑刃脚形状和切土深度,建立沉井下沉过程中极限土阻力的近似计算模型。基于Prandtl问题的滑移线场理论,建立考虑刃脚切土深度和刃脚形状的近似滑移线场,并导出平面应变和圆形沉井轴对称问题极限承载力系数的计算公式。对于平面应变问题,承载力系数Nγ等于两部分之和,即不考虑切土深度时刃脚踏面和考虑切土深度时刃脚内侧倾斜面对承载力的贡献,前者及其他两个承载力系数(黏聚力和超载项)与不考虑刃脚切土深度由Prandtl承载力机制所得的结果相同。刃脚的切土深度、踏面宽度和倾斜角是影响极限土阻力的重要因素,忽略刃脚切土深度及其范围内刃脚倾斜面与土的作用将导致极限土阻力的计算值明显偏小。分析结果表明,承载力系数随刃脚切土深度和刃脚倾斜角的增加而显著增大;若土体强度较高,刃脚倾斜角的大小对极限土阻力的影响更加显著。

An approximation model to evaluate the limiting soil resistance beneath the cutting curb during sinking of an open caisson is investigated,in which the shape and embedment depth of the cutting curb are considered.And then a typical slip line field for this problem is presented approximately with Prandtl failure mechanism;and the formulas of bearing capacity factors are derived for the plane strain problem and axisymmetric one of a circular open caisson,respectively.For the plane strain problem,the bearing capacity factor Nγ is composed of two parts: one part is caused by the tread of cutting curb;and the other one is the inclined plane,and the former,as well as the other bearing capacity factors,Nc and Nq,are identical with the results derived from Prandtl failure mechanism when the embedment depth of cutting curb is not considered.The embedment depth and width of tread and taper angle of the cutting curb exert a major influence on the limiting soil resistance.If neglecting these influence factors,the evaluated value of the limiting soil resistance would be significantly small.This study shows that the values of bearing capacity factors increase significantly with the increase of the embedment depth or taper angle of cutting curb.And it also shows that the taper angle has a more significant influence on the limiting soil resistance when the strength of soil is relatively high.