考虑应力扩散时桩端土性对单桩沉降影响分析方法

基于虚土桩模型，分析了层状地基中桩端土性对单桩沉降特性的影响。首先，以虚土桩扩散角反映桩端土层应力扩散效应，将桩端一定锥角范围内由桩端至基岩面的土体视为虚土桩，并根据其变截面特性，将虚土桩沿纵向划分为有限个微元段。然后，对桩及虚土桩桩侧土体采用理想弹塑性荷载传递模型，利用荷载传递法，推导了层状地基中以桩侧土塑性发展深度为变量的单桩荷载-沉降递推计算方法，并进一步得到了桩身轴力及桩侧摩阻力递推计算式。在此基础上，给出了荷载传递模型参数选取方法，并分析了虚土桩临界深度的影响因素及由实测荷载-沉降曲线反演虚土桩扩散角的可行性。最后，利用该方法分析了桩端沉渣和软弱下卧层对荷载-沉降曲线的影响。结果表明，考虑桩端土层应力扩散效应时，通过计算得到的桩顶及桩端荷载-沉降曲线与实测曲线吻合较好；当桩端存在沉渣或软弱下卧层时，采用虚土桩模型的单桩沉降计算方法可以在一定程度上反映沉渣特性及软弱下卧层埋深等因素对桩顶荷载-沉降曲线的影响。

A new method for analyzing influence of pile tip soil properties on single pile settlement considering stress dispersion

Based on virtual soil-pile model, the influence analysis of pile tip soil properties on single pile settlement is conducted in terms of layered soils. Firstly, considering stress dispersion in soil medium, the soil between pile tip and bedrock surface is assumed to be virtual soil-pile. Furthermore, the virtual soil-pile with variable cross-section is divided into finite segments. Then, the surrounding soil layers of pile is modeled as ideal elastoplastic transfer model; and regarding the developmental plastic depth as an independent variable, a recursive method for calculating axial force and side friction of pile in layered soil is derived by load transfer method. On this basis, parameters selection of load transfer model is studied; meanwhile, the factors of virtual soil-pile length and the feasibility of acquiring stress dispersion angle through inversion analysis are analyzed. Finally, by means of the presented method, the difference of load-displacement curves has been examined when pile bottom sediment and soft substratum exist. The results show that: the calculated load-displacement curves of pile tip and pile top agree well with the measured curves considering stress dispersion of pile tip soil; the presented method can take the influences of pile bottom sediment and soft substratum on load-displacement curves into consideration.