Analysis, interpretation and prediction of the structural behavior of Cahora Bassa dam (Mozambique), affected by concrete swelling

Abstract

This paper presents the analysis, interpretation and prediction of the structural behavior of Cahora Bassa dam, which concrete is affected by a moderate ongoing swelling process, of the alkali-silica (ASR) type. To estimate the evolution of the dam’s concrete swelling for a medium-term horizon, the performed analysis took into account 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. The interpretation of the dam’s behavior over time and its prediction for the next decade was based on mathematical modeling, using a three-dimensional model of the dam and of the rock mass foundation, solved by the finite element method. All relevant actions on the structures were considered, namely the dead weight of the materials, the prestress connecting the mid-bottom spillway structures to the dam’s body, the hydrostatic pressure, 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 the stress state on the development of the expansions. The monitored values and the numerical results showed an excellent agreement until 2020, attesting the adequacy of the models used to simulate the dam’s behaviour. The expansions will continue to have a central role in the dam's behavior. The stress fields, computed in the dam´s body and in the midbottom spillway structures, have a higher relevance in the abutment bearings, near the crest.