Influence of temperature and stress field seasonal variations in the development of concrete swelling in dams. Application to the case of Covão do Meio dam (Portugal)

Abstract

This paper presents the study of the influence of temperature and stress field seasonal variations in the development of concrete swelling in dams, considering the case study of Covão do Meio arch dam, in Portugal, which concrete is affected by a moderate ongoing swelling process, of the alkali-silica (ASR) type, and which reservoir empties every year in the dry season. In a first step, a three-dimensional model of the dam and of the rock mass foundation, solved by the finite element method, was used for the interpretation of the dam’s behaviour over time. All relevant actions on the structure were considered, namely the dead weight of the materials, the hydrostatic pressure on the upstream face, the temperature changes in the dam’s body and the concrete expansions of internal origin. The structural model considered the concrete viscoelastic behaviour and the influence of temperature and stress fields in the expansion development. The results of the dam’s monitoring, of the concrete laboratory tests for diagnosis and prognosis of the concrete properties and of the visual inspections were considered. The monitoring and the numerical results showed an excellent agreement until 2020, attesting the adequacy of the models to simulate the dam’s behaviour. In a second step, the dam’s behaviour was simulated considering that the reservoir remains at high levels throughout the year, during all the lifetime of the dam. In this scenario, the computed expansions and its related structural effects decreased of about 10% to 40%, namely in terms of displacements and stresses. It is concluded, therefore, that the decompression of the dam body and the concrete temperature raise, associated to the reservoir lowering during a significant period of the year, has a great influence