Prediction of the structural behaviour of Bemposta dam (Portugal), affected by concrete swelling

Abstract

This paper presents the case study of the Bemposta dam, a hollow arch-gravity structure, whose concrete is affected by moderate expansive alkali-silica reactions. To interpret the dam behavior and the effects of the expansive reactions, a structural model was developed, considering the evolution of the concrete properties, including creep and relaxation, and the evolution of the main actions, namely the hydrostatic pressure, the temperature variations and the expansions. The temperature variations in the dam’s body were computed using a thermal model, considering the air and the water temperatures and the solar radiation on the dam’s external surfaces. A remarkable adjustment was obtained between the structural model and the monitored displacements, which allowed to validate the numerical models. The obtained results show that the swelling effects are already dominant on the dam behavior, both in terms of the horizontal and vertical displacements and in terms of the stress fields. Based on the developed models and on two estimates for the expansion’s evolution, an optimistic one, in which the expansions stabilize in the short term, and a pessimistic one, in which the remaining potential for expansion is still significant, two scenarios were established that enclose the behavior of the dam for the next 20 years.