Laboratory Model Study on the Pile-Forming Mechanisms and Bearing Deformation Characteristics of CFA Piles

Deliang Zhu,Lingwei Zheng,Xinyu Xie,Pengfei Fang,Yue Li,Jian Zhang

doi:10.1155/2021/4827596

Abstract

To study the pile-forming mechanism and bearing deformation characteristics of continuous flight auger (CFA) piles, a series of procedures, including helical drilling, pulling up/grouting, and inserting cage/pile forming, were simulated in clay-sand double-layer foundations by a homemade model drilling machine system in laboratory model tests. The effects of two different pile-forming methods on the load transfer and bearing characteristics of the piles were investigated by performing a model test comparison of CFA piles and bored piles. The experimental results show that there exist a soil improvement effect around the pile and a diameter expansion effect during the drilling process and grouting process for the CFA pile, which can effectively improve the lateral friction resistance of the pile. Compared with the bored pile, the pile diameter in the middle of the CFA pile increased by 19%, and the total lateral friction resistance of the CFA pile increased by 9.1% at a high load (1500 N). The comparative results of the model tests show that the bearing capacity of a single CFA pile increased by 50.0% and that the total settlement decreased by 40.5%. The results of the in situ test piles show that the load-settlement curves of the two pile types are similar under low-medium loads and that the lateral friction resistance of the CFA pile under high loads is better developed, which is relatively consistent with the model test results.

Highlights

Continuous flight auger (CFA) piles, which are known as augered cast-in-place (ACIP) or auger-cast piles, comprise a new construction method for pile foundations
To ensure that the conditions of the two types of piles are consistent in the comparison test, the CFA pile and bored pile are formed in the same ground model, and the pile ends are embedded into the sand layer at a depth 0.1 times the pile diameter
Comparative model tests were performed on CFA piles and bored piles, and the pile-forming mechanism and bearing deformation characteristics of the CFA pile were further analyzed based on the static load test results of the field engineering test pile

Summary

Introduction

Continuous flight auger (CFA) piles, which are known as augered cast-in-place (ACIP) or auger-cast piles, comprise a new construction method for pile foundations. In terms of numerical analysis, Jozefiak et al [11] established a calculation model of pile-soil systems with ABAQUS software, which fits well with the field static load test results of CFA piles. E former adopts the static load and presses the model piles into the soil, while the latter sets the premade piles in the designed position followed by clay filling, which differs from the pile-forming method utilized in this paper. Compared with these two methods of pile formation in model tests, the construction technology and pile formation process of CFA piles have a greater impact on the bearing deformation characteristics of a pile. The bearing mechanism and bearing performance of CFA piles are measured by field tests

Model Test

Analysis of the Results

Pile-Forming Mechanism and Engineering Case Analysis

Findings

Conclusions