A Novel Numerical Method for Calculating Vertical Bearing Capacity of Prestressed Pipe Piles

Rongbao Chen,Meixiang Gu,Jichao Zhang,Zeyu Chen

doi:10.1155/2020/8828587

Abstract

A novel method for calculating the vertical bearing capacity of prestressed pipe piles with the acceptable error was proposed and verified. Soils at the pile side and end were, respectively, simulated by an elastic-plastic model and a new double-line (at soft rock and soil layers) or triple-line model (at hard rock and soil layers); then, a mechanical model was established for simulating vertical bearing capacity of prestressed pipe piles, and the corresponding calculation process was carried out. The values of pile side resistance, pile end resistance, and pile end elastic displacement were first obtained from the results of high-strain dynamic testing (HSDT) and then were imported into the proposed numerical model for calculating the vertical bearing capacity of prestressed concrete pipe piles. The static load test was carried out to verify the numerical results. Besides, 20 piles were tested at two typical test sites (soft and hard rock bearing strata), of which 8 piles were arranged at the soft rock bearing stratum site and 12 piles were arranged at the hard rock bearing stratum site. The numerical results achieved from an empirical formula were also used for making a comparison. The values obtained by the proposed method were highly close to those achieved from the static load test with an error of within 10%. The outcomes indicated that the proposed numerical method can be potentially applied to predict the bearing capacity of prestressed pipe piles.

Highlights

In a number of countries, especially in China and Japan, prestressed concrete pipe piles have become one of the most important types of pile. e theoretical solutions employing the bearing capacity to calculate the pile shaft and tip resistance involve setbacks caused by uncertainty factors, such as installation method, stress history, and soil compressibility [1]. e experimental tests, such as standard penetration test (SPT), static cone penetration test (CPT), and static load test (SLT), correlating results of in situ tests with the bearing capacity of pile, are frequently used in evaluating load-bearing capacity of a single pile; note they involve shortcomings induced by both operator and test procedure [2]
A new type of offshore oil and gas platform mixed pile was explored with the laboratory test program and the finite element model (FEM), and the results show that the novel offshore foundation type is suitable for a wide range of sand conditions [25]. e influences of sand piles on improving the bearing capacity of soil foundations as well as controlling the settlement have been studied by partially replacing sand piles with constraints [26]
To explain the principle of high-strain dynamic testing (HSDT) that was employed in this research and the results that are presented in Figures 9(a)–10(d), the analysis of pile #1 in Figure 9(a) is taken as an example. e satisfactory agreement between solid line and dashed line (top-left corner subfigure in Figure 9(a)) indicates acceptable results of field testing. e solid line represents the results of field testing, and the dashed line shows the results of numerical simulation. e top-right corner subfigure in Figure 9(a) illustrates the excitation profiles at the end of pile. e bottom-left corner subfigure in Figure 9(a) displays the pile top displacements

Summary

Introduction

In a number of countries, especially in China and Japan, prestressed concrete pipe piles have become one of the most important types of pile. e theoretical solutions employing the bearing capacity to calculate the pile shaft and tip resistance involve setbacks caused by uncertainty factors, such as installation method, stress history, and soil compressibility [1]. e experimental tests, such as standard penetration test (SPT), static cone penetration test (CPT), and static load test (SLT), correlating results of in situ tests with the bearing capacity of pile, are frequently used in evaluating load-bearing capacity of a single pile; note they involve shortcomings induced by both operator and test procedure [2]. E theoretical solutions employing the bearing capacity to calculate the pile shaft and tip resistance involve setbacks caused by uncertainty factors, such as installation method, stress history, and soil compressibility [1]. The blow count (N) of SPT (SPT-N), the number of blows to drive a sampler mm in the ground, may significantly vary due to the various experimental and operational conditions in the preliminary investigation of a project site [3], and the SPT-N is widely applied in predicting bearing capacity and assessing the quantificational risk of soil liquefaction [3,4,5].

Methods

Results

Conclusion