On distributed strains in a CFA pile via DFOSs measurements and numerical analysis

Fibre Optic Sensors (FOSs) offer unprecedented possibilities for the monitoring of engineering structures, such as foundation systems. Notably, the type of FOSs known as Distributed Fibre Optic Sensors (DFOSs) has the capability of monitoring variations in the observed physical field, such as strain and temperature, with spatial continuity along the fibre. This paper presents and discusses the distributed strain measurements collected along a continuous flight auger (CFA) pile, belonging to the foundation raft of a new bridge subjected to an acceptance static load test. The monitoring was performed using a DFOS system, which works according to the optical frequency domain reflectometry (OFDR) method and provides a spatial resolution of 10 mm and a strain resolution of 1 με. The in-situ monitoring results were used to calibrate a 3D Finite Element Model of the foundation system. The soil properties for the numerical model were also selected on the basis of a load test previously carried out on a similar pile at the same site