Distributed fibre optic sensors for measuring strain and temperature of cast-in-situ concrete test piles

In this paper we present the use of distributed fibre optic sensor (DFOS) technology to measure the temperature and strain of reinforced concrete test piles during construction and during static load tests. Eight test piles were recently instrumented with DFOS, on three construction sites in London, by the Cambridge Centre for Smart Infrastructure and Construction (CSIC), in collaboration with Ove Arup & Partners Ltd. The concrete curing temperature profiles of the piles were used to detect the presence of significant defects in the piles. The load test strain profiles along the length of the piles were used to determine the load capacity of the piles and estimate the design parameters of the various soil strata, as well as the internal relative displacement of the piles under various loads. Being distributed in nature, DFOS give a much more detailed picture of the performance of a test pile, as compared to traditional embedded point sensors, such as vibrating wire strain gauges and extensometers. This is demonstrated with a sample of data obtained from one of the instrumented test piles.