Distributed fiber optic monitoring of a CFA pile with a central reinforcement bar bundle

Abstract

In this paper, we present an application of distributed fiber optic sensor (DFOS) technology to measure the strain of a continuous flight auger (CFA) test pile with a central reinforcement bar bundle, during a static load test carried out in London. Being distributed in nature, DFOS gives much more information about the pile performance as compared to traditional point sensors, such as identifying cross-sectional irregularities or other anomalies. The strain profiles recorded along the depth of the piles from the DFOS were used to calculate pile deformation (contraction), shaft friction, and tip resistance under various loads. Based on this pile load test, a finite element (FE) analysis was performed using a one-dimensional nonlinear load-transfer model. Calibrated by the shaft friction and tip resistance derived from the monitored data, the FE model was able to simulate the pile and soil performance during the load testing with good accuracy. The effect of the reinforcement cage and central reinforcement bar bundle were investigated, and it was found that the addition of a reinforcement cage would reduce the pile settlement by up to 20%.

Keywords

continuous flight auger pile / static load test / central reinforcement bar bundle / distributed fiber optic sensor / finite element / load transfer

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Acknowledgement

The authors thank the EPSRC and Innovate UK for funding this research through the Cambridge Centre for Smart Infrastructure and Construction (CSIC) Innovation and Knowledge Centre (EPSRC grand reference number EP/L010917/1). We thank Professor Kenichi Soga (UC Berkeley) for providing valuable input to this research. We would also like to acknowledge the contribution of Angus Cameron from Environmental Scientifics Group.

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