考虑路堤-加固区相互作用的刚性桩复合地基沉降算法

Settlement calculation method of rigid pile composite foundation considering interaction between supported embankment and improved zone

为合理计算路堤荷载作用下刚性桩复合地基沉降,考虑路基填土中的土拱效应以及路堤-地基加固区竖向荷载传递的耦合特征,基于填土中内、外土柱界面摩阻力系数随深度线性发挥模式以及复合地基中桩土相对位移模式与桩侧摩阻力系数分布模式,采用微元体静力平衡原理,并考虑路堤-加固区-下卧层之间的应力连续与变形协调条件,推导出了路堤下刚性桩复合地基的桩土应力比、桩土沉降差、加固区沉降量的计算公式,定量反映了路基填高、填土及软土地基的黏聚力和内摩擦角、桩长、桩径、桩间距等多个主要因素。实例分析表明,加固区沉降量的计算值与实测值误差一般不超过15%;桩长对加固区沉降呈非线性影响;面积置换率、地基土内摩擦角与黏聚力对加固区沉降均具有线性的负相关影响特征,且沉降量受内摩擦角影响比黏聚力更敏感。

In order to accurately calculate the settlement of rigid pile composite foundation under embankment load,an analysis method is provided based on vertically linear development model of friction coefficient between the inner and exterior soil columns in the embankment supported by the composite foundation,as well as distribution mode of pile-soil relative displacement and development coefficient of skin friction on the pile.Thus,considering soil arching effect in the embankment and coupling characteristics of vertical load transfer between the embankment and improved zone,pile-soil stress ratio,differential settlement between pile and soil,and settlement of the improved zone are all derived by the principle of static equilibrium of a microelement in the embankment-foundation system.The proposed method can quantitatively reflect the dominant influence factors,such as height of embankment,internal friction angle and cohesion of the filling and soft foundation soil,pile length,pile diameter and pile spacing.Analysis results of examples show that relative error between the calculated and measured values is less than 15%.Pile length has non-linear effect on the settlement of the improved zone,while area replacement ratio,cohesion and internal friction angle of the foundation soil have linearly negative effect on the settlement.Moreover,the settlement is more sensitive to internal friction angle than cohesion.