Distributed Fibre Optic Sensing for Monitoring Reinforced Concrete Piles

Abstract

Distributed fibre optic sensing (DFOS) presents several advantages over traditional point sensors, for measuring strain and temperature in civil and geotechnical infrastructure. DFOS techniques use light transmitted through an optical fibre to enable measurements to be taken all along an embedded or surface-mounted fibre optic cable, which can be up to several kilometres long. This makes DFOS particularly useful for monitoring linear structures and to detect the potential existence of any anomalies which are usually unpredictable. Hence, DFOS has gained in popularity for monitoring reinforced concrete piles, especially during pile testing.
The spatially continuous strain data from DFOS provide detailed information about load transfer along the pile but can also be used to calculate vertical displacements and shaft friction through numerical integration and differentiation, which are useful for validating relevant performance-based numerical models. This paper introduces the methodology and illustrates these advantages through an example obtained from an instrumented pile load test in London. While it synthesises a number of lessons learned in the application of DFOS for pile testing, it also supports the case for routine long-term monitoring of working piles.