Displacement Monitoring in Cabril Dam Using GNSS


Miguel Rodrigues(1), Sérgio Oliveira(2), José Nuno Lima(3) & Jorge Proença(4)


Abstract: 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 plumblines, geodetic methods or, more recently, with GNSS (Global Navigation Satellite System). For Cabril dam – the case study presented in this paper – no plumblines were installed in the central section. Thus, the displacement monitoring in this section is carried out using classic 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 has presented cracking problems since first filling it is important to continuously monitor several notable points, which include 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 on the upper zone is simulated through joint elements. The 3D FE model was calibrated based on the displacements observed by plumblines (in two non-central sections), and by classic geodetic methods considering variations in hydrostatic pressure and annual temperature. The displacement evolution observed by the plumbline 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 3D FE model was firstly calibrated using plumbline results, and then used to validate the GNSS measurements.


Keywords: Arch dam, monitoring, safety control, Global Navigation Satellite System, measuring displacements, HSCT model, 3D FEM.


1. Introduction


Large concrete dams are potentially high risk structures whose safety control requires continuous monitoring. Safety control in most dams comprehends the displacement


Author Details: (1)Laboratório Nacional de Engenharia Civil, Portugal. Email: miguel.ads.rodrigues@gmail.com; (2)Laboratório


Nacional de Engenharia Civil, Portugal. Email: soliveira@lnec.pt; (3)Laboratório Nacional de Engenharia Civil, Portugal. Email: jnplima@lnec.pt; (4)CERIS - Instituto Superior Técnico, Portugal. Email: jorge.m.proenca@tecnico.ulisboa.pt


This paper was originally presented to delegates who attended the Dam World Webinar on 22-24 September 2020 (https://dw2020.lnec.pt/dw-webinar). For further information please contact the organisers via email: damworld@lnec.pt


Vol XXXI Issue 3 DAM ENGINEERING 149


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