Displacement monitoring in Cabril dam using GNSS

Abstract

The continuous displacement monitoring is essential for the safety control of large dams. It should be based on the comparison between numerical model results and monitoring data, e.g. observed displacements using plumb lines, geodetic methods or, more recently, with GNSS (Global Navigation Satellite System). For Cabril dam, the case study presented in this paper, no plumb lines were installed in the central section. Thus, the displacement monitoring in this section is carried out by classical geodetic methods that do not allow continuous monitoring (only two observation campaigns per year). So, in this case, the use of GNSS was considered particularly useful, as it allows continuous monitoring of displacements at the top of the central section. As Cabril dam presents cracking problems since the first filling, it is important to continuously monitor several notable points, which includes the point at the top of the central section. The present work focuses on the validation of the displacements obtained by GNSS, at Cabril dam, using a 3D finite element model, developed in MATLAB, in which the horizontal cracking at the upper zone is simulated through joint elements. The 3DFE model was calibrated based on the displacements observed by plumb lines (in two non-central sections) and by classical geodetic methods, considering variations in hydrostatic pressure and annual temperature variations. The displacement evolution observed by plumb lines and geodetic methods were analyzed using HSCT (Hydrostatic, Seasonal, Creep and other Time effects) separation of effects models, to facilitate the comparison process between the observed displacements and the numerical results. In this way, the 3DFE model was firstly calibrated using plumb lines results and then it was used to validate GNSS measurements.