Development of a biaxial fibre Bragg grating (FBG) extensometer with axis misalignment error compensation and cloud integration for advanced slope monitoring

Abstract In the paper, an FBG-based biaxial extensometer is presented to detect ground movement, which is a crucial element in slope monitoring systems. Multiple FBGs were used as displacement sensors to establish sensing nodes at various locations along an HDPE pipe. Each sensing node comprises two FBGs for biaxial displacement measurement. A numerical model based on characterization matrix equation is formulated to estimate the lateral displacement vectors using the displacement data obtained from all FBG sensors. The inclusion of torsion effects in the characteristic matrix equation addresses the misalignment error in the principal axis at each sensing node, thereby enhancing estimation accuracy. Through characterization tests, there is a notable enhancement in the accuracy of the displacement vector estimation. Finally, the proposed extensometer is being examined to determine if it can be integrated with the cloud network for remote monitoring. Various random displacement shapes and curvature angles have been tested. The results demonstrate a strong similarity between the shapes reconstructed by the model and the actual ones.