A simplified nonlinear calculation method to describe the settlement of pre-bored grouting planted nodular piles

Abstract

The pre-bored grouting planted nodular (PGPN) pile is a type of composite pile foundation that is considered to be environmentally friendly and economical. A simplified approach, which considers the two interfaces of the pile shaft, was proposed to analyze the load-displacement response of a single PGPN pile. An elastic-failure model, based on the shear test results, was used to simulate the shearing behavior of the concrete-cemented soil interface. A hyperbolic nonlinear model, considering the influence of cement paste injection, was created to simulate the behavior between the skin friction and the relative displacement developed along the cemented soil-soil interface. A linear model and a nonlinear model that considers the reduction in the shearing stiffness were used to simulate the PGPN pile base load-displacement responses in a field test and in a model test, respectively. Comparisons between the calculated and measured load-displacement responses revealed relatively good agreement. The proposed approach is thus shown to be efficient and suitable for the analysis of a single PGPN pile embedded in layered soils, and is used to analyze the factors influencing its behavior. Enlarged cemented soil base is considered to be effective in promoting the behavior of a short PGPN pile, while increasing the diameter of cemented soil along the shaft is efficient in promoting the compressive bearing capacity of a long PGPN pile.

中文概要

目的

静钻根植竹节桩是一种由预制桩和水泥土组成的组合桩基, 其桩身具有预制桩-水泥土和水泥土-桩周土体两个接触面。本文以桩土接触面剪切试验、模型试验和现场试验数据为基础, 提出一种静钻根植竹节桩简化沉降计算方法, 为静钻根植竹节桩的沉降计算提供依据; 并通过所提出的简化计算方法对静钻根植竹节桩桩端水泥土扩大头以及桩周水泥土直径对静钻根植竹节桩承载性能的影响进行研究。

创新点

1. 通过剪切试验对预制桩-水泥土接触面的剪切性能进行研究, 得到接触面侧摩阻力与相对位移的关系; 2. 建立同时考虑预制桩-水泥土接触面和水泥土-桩周土体接触面作用的静钻根植竹节桩简化沉降计算方法。

方法

1. 通过桩土接触面剪切试验, 得到预制桩-水泥土接触面摩擦模型; 2. 通过对模型试验结果的分析, 得到水泥土-桩周土体接触面摩擦模型; 3. 根据试验结果编写静钻根植竹节桩沉降计算程序, 通过与试验结果的比较验证所提计算方法的可靠性; 4. 通过提出的静钻根植竹节桩简化计算方法对静钻根植竹节桩承载力影响因素进行分析与研究。

结论

1. 预制桩-水泥土接触面摩擦性能远优于水泥土-桩周土体接触面摩擦性能; 2. 由于水泥浆的渗透作用, 水泥土-桩周土体接触面的初始剪切刚度有所提高; 3. 所提出的计算方法能够有效地计算出静钻根植竹节桩单桩在成层土体中的荷载位移关系曲线; 4. 桩端水泥土扩大头能够有效地提高静钻根植竹节桩桩端承载性能, 并且增加桩周水泥土直径能够提高静钻根植竹节桩承载性能。