Practical Analysis and Assessment of AAR Affected Dams and Hydroelectric Plants

Abstract

Hatch has been involved in many hydro projects where alkali aggregate reaction (AAR) has affected dams and power plants. AAR causes the concrete to expand and this leads to issues including reduction in spillway and intake gate clearances, concrete cracking, high compressive and shear stresses in concrete substructures, stressing of turbine embedded parts and turbine/generator alignment problems. During the course of these investigations, a practical finite element program (GROW3D) has been developed to analyze the effects of concrete expansion on these structures. The program is based on relatively simple engineering principles yet it has proven to be a reliable tool in the prediction of the structural behavior of dams and power plants. The objective of this paper is to present selected results from recent analyses performed on the Mactaquac Dam and power plant which is located in New Brunswick, Canada. The stress-dependant concrete growth law used in GROW3D has recently been modified to better match the observed behavior of the Mactaquac intake structure response to slot cutting. The new concrete growth law was subsequently used in a global finite element analysis of the Mactaquac powerhouse and the results of the analysis provided an excellent match to measurements of structural and mechanical AAR-induced deformations. Finally, the powerful effect of differential concrete expansion in structural elements is examined using simple analytical methods.