Calculation of Negative Frictional Resistance of Foundation Pile in Deep Fill Foundation

Ningyu Zhao,Shun Xiang,Yi Song,Hongjun Wu,Hussein Abulkasim

doi:10.1155/2021/6640777

Ningyu Zhao, Shun Xiang + Show 3 more

Open Access

https://doi.org/10.1155/2021/6640777

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Abstract

In deep fill foundations, the pile foundation might suffer from negative frictional resistance (NFR) due to the consolidation and settlement of the soil. The NFR will cause the pile to settle excessively and reduce its bearing capacity. However, there are not yet many accurate methods to calculate the NFR of foundation piles in deep fill foundations. To make up for the gap, this paper carries out shear tests on the pile-soil interface and discusses the mechanism of pile-side frictional resistance. Considering the distribution law of pile-side frictional resistance with depth, the authors proposed a piecewise calculation model for pile-side frictional resistance, which couples the hyperbolic model and effective stress method. Then, the energy balance equation of the pile when the NFR occurs was established in the light of the energy transfer of the pile-soil system during the settlement of the soil around the pile. Furthermore, the calculation formulas of the axial force and displacement of the pile at different depths were derived, considering the pile-soil displacement and the potential energy change of the pile-soil system. The proposed method was applied to calculate the NFR of the foundation pile in a construction site, and the calculated results were compared with the measured data. The results show that the axial force-depth curve of the pile obtained through theoretical calculation agrees well with the measured data. Hence, our method can accurately reveal the mechanical features of the pile foundation in deep fill foundations.

Highlights

In mountainous and hilly areas, the foundation of construction sites often features undulating bedrock surfaces and deep fills
E relative displacement between the pile and the soil has a great impact on the distribution and magnitude of the pile-side frictional resistance, especially at the neutral point. e calculation of pile-soil displacement is very important for accurately predicting the influence of the pull-down load caused by negative frictional resistance (NFR) on the bearing capacity design of the pile foundation
Chen et al [2] proved that the pile-side NFR can be simplified into a linear model by the effective stress method

Summary

Introduction

In mountainous and hilly areas, the foundation of construction sites often features undulating bedrock surfaces and deep fills. Prior to the construction of the pile foundation, the filling site usually undergoes years of foundation treatments, such as self-weight consolidation and dynamic compaction Most of these deep fills have completed consolidation and settlement, negative frictional resistance (NFR) will be induced by the compressive deformation and incomplete consolidation of the foundation soil. Considering the effects of effective stress and pile-soil displacement on pile-side frictional resistance, He et al [7] established a calculation model for the friction on the side of the rock-socketed pile by the load transfer method and iteratively computed the analytical solution of the axial force and the solution of power series for pile displacement. Based on the reciprocal theorem, the control equations of the axial force and displacement of the pile were derived under different pile-soil displacements and solved by the iterative method. e proposed method was proved feasible and accurate by comparing the calculation results with the measured data

Calculation Models

Building and Solving Energy Balance Equations

Comparative Analysis