MIGUEL RODRIGUES, SERGIO OLIVEIRA, JOSE NUNO LIMA & JORGE PROENCA


evolution analysis of some notable points. At Cabril dam the displacements in the upper central zone are measured bi-annually using geodetic methods. Due to the curvature of the dam it was not possible to install plumblines to measure that specific zone’s displacements, which is one of the reasons why the decision was made to install a Global Navigation Satellite System (GNSS) to measure displacements at that location. The GNSS system was installed at Cabril dam (Figure 1) in 2016 by LNEC and EDP as part of a project financed by FCT. The decision to install this system was also influenced by the fact that Cabril dam presents horizontal cracking near the crest, which was detected during first filling and occurred because the dam thickness increases near the crest causing vertical tensile stresses at the downstream face due to high hydrostatic pressures (from high reservoir levels). Gel exudations were also identified in the upper gallery, indicating the existence of swelling reactions.


Figure 1. Cabril dam. GNSS antenna location at the top of the central cantilever and 3D FEM discretization


2. Use of GNSS for Displacement Monitoring in Arch Dams


A Global Navigation Satellite System (GNSS) instantly determines the position and velocity of an observer with accuracy, and at low cost, anywhere on the Earth’s surface. This explains why GNSS is the most used navigation system.


The main purpose of navigation is to determine the position and speed of a given point in a well-defined coordinate reference. Tests carried out at the LNEC campus confirmed that by using the same equipment 24 hours a day, and under any weather conditions, GNSS was


150 DAM ENGINEERING Vol XXXI Issue 3


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