Abstract: Based on strain measurements from distributed fiber-optic sensors (DFOSs), an inversion method for discontinuous buried pipelines is proposed to predict the deflection and gap formation induced by tunnel excavation. The double-layer Winkler foundation beam model, which takes into account the relationship of bending moment-joint rotation, is employed to investigate the pipeline-soil interaction. The inversed pipeline deflection, rotation, and soil settlement are derived by utilizing the finite difference method and the conjugate beam method, respectively. Furthermore, the extent and location of the interface void are also identified. The inversion accuracy is verified in comparison with the numerical solution of the finite element method. Results show that the influence of joint rotational stiffness on the response lies within a certain range, which is seldom influenced by the pipeline flexural stiffness. The void range increases with the pipeline flexural stiffness and soil settlement. The upper void is likely to occur for an overlying subgrade with a large reaction coefficient, while the lower void is likely for an underlying subgrade. The combined boundary conditions of rotation angles at both endpoints and the position of maximum strain result in high inversion accuracy and markedly improve the anti-noise performance.

Key words: distributed fiber optic sensor, buried pipeline, tunnel, double-layer Winkler foundation, inversion, interface void