Monitoring 3D movement of structures and soil masses using fiber optic cables under the notion of finite element method

Conventional methods and Distributed Fiber Optic Sensing (DFOS) are increasingly adopted in monitoring soil-structure interaction projects (pile foundations, retaining structures, underground stations). Despite their wide application in two-dimensional (2D) problems, a straightforward applicability to three-dimensional (3D) cases has not proved feasible. With the aim to extend the applicability of DFOS in Civil Engineering projects experiencing three-dimensional movements such as large dams, tunneling and many other cases where soil deformations are determinant for the response of related structures, a new method is proposed in this paper. The fundamental principle of the method arises from the use of the notion of the Finite Element Analysis (FEA), where the real space of a fiber optic carrier is subdivided to elements bijectively related to a master element. The method was implemented in a Python code and validated against a simplified two-dimensional laboratory test associated with high resolution data (±1.0 με) and noiseless strain data generated from 3D finite element analyses. The sensitivity of the method to noisy data, associated with realistic conditions and the resolution of DFOS analyzers, was further investigated, revealing the limits of the method’s applicability and the factors affecting the accuracy and reliability of the resulting 3D displacement predictions.