Automated ultra-weak Fiber Bragg Grating (uwFBG) shape sensing for 3D internal deformation monitoring of earth-rockfill dams

Internal deformation monitoring of earth-rockfill dams is crucial for ensuring safe operation. Although fiber optic shape sensing offers advantages in distributed deformation monitoring, its engineering application in such dams is hindered by complex deformation patterns, long-distance error accumulation, and uncertainties in strain transfer. To address this problem, this paper proposes an internal deformation monitoring method by integrating ultra-weak Fiber Bragg Grating (uwFBG) with a simplified three-dimensional inverse Absolute Nodal Coordinate Formulation (iANCF S3D). The iANCF S3D ensures high computational accuracy under complex deformation conditions. The uwFBG-based deformation sensor and the standardized installation method are developed to transform complex distributed loads into discrete loads, thereby ensuring long-distance computational accuracy while ensuring effective strain transfer. Model tests indicate that the measurement error is within 5%, and field application in an earth-rockfill dam demonstrates reliable performance. This method provides an economical, reliable, and efficiently deployable automated monitoring solution for earth-rockfill dam deformation monitoring.