Distributed strain measurements in a CFA pile using high spatial resolution fibre optic sensors

Static load tests on fully instrumented piles are a useful tool for optimizing the design of pile foundations. By measuring the change in strain along a test pile it is possible to estimate pile-soil interface properties and infer site-specific and technology-specific load-transfer curves to be adopted for design. This paper presents strain measurements obtained from a distributed sensor installed in a continuous flight auger (CFA) pile undergoing a static load test. Distributed sensing was performed using optical frequency domain reflectometry (OFDR), which provided a spatial resolution of 10 mm. The high spatial resolution allowed to highlight local defects, as those produced by undesired variations in the pile cross-section area that can lead to erroneous data analysis if not fully understood. The paper also presents an approach for the derivation of load-transfer curves from continuous strain data.