Updating of the behaviour analysis and interpretation of Cahora Bassa dam (Mozambique) considering the mid-bottom spillway structures

Abstract

This paper presents the updating of the behaviour analysis and interpretation of Cahora Bassa dam, a 166 m high double-curvature arch dam, located in the Zambezi river (Mozambique). The structural numerical model includes, in addition to the dam’s body with the mid-bottom spillway holes, already considered in the previous studies, the downstream structures of that spillway. The results computed with the updated structural model together with the data provided by the dam monitoring system, support the analysis and interpretation of the dam behaviour, since the first filling of the reservoir, occurred in 1974, up to the end of 2016. The structural model, based in 3D finite elements of the dam and its foundations, takes into account the concrete viscoelastic behaviour, the variation of the reservoir level and the expansions due to the moderate alkali-aggregate reactions (AAR) on the dam´s concrete. The monitoring and the numerical results display an excellent agreement, showing the suitability of the finite element model for modelling the dam’s behaviour. Additionally, the obtained results confirm the relevance and influence of creep and swelling effects in the dam structural response. Relatively to the stress fields, the computed results show that at the arch bearings the stresses assume already significant values. The displacements computed at the mid-bottom spillway structures are important data for verifying the operation of the gates.