Condition and Structural Assessment of a Nearly 100 Year Old Arch Dam Affected by ASR

The single-curvature arch dam with a maximum structural height of approx. 25 m was constructed in the early 1920’s and deterioration was observed shortly after. The cause of deterioration was assessed to be concrete growth in the 1950’s and alkali-silica reaction as root cause was confirmed in the 1960’s. Several condition assessments were carried out since deterioration begun that confirmed ongoing deterioration due to ASR which led to the asset owner’s decision to plan the replacement of the dam in the near future. To assess the current structural integrity and predict the residual life of the structure a detailed investigation was carried to assess the physical concrete properties, rate of deterioration and to determine potential failure modes. The physical concrete properties did not appear to have deteriorated over the last 30 years despite ongoing confirmed horizontal and vertical displacement which has increased leakage resulting in an accelerated rate of freeze-thaw attack. The numerical model identified the dam to be stable but hinges had already formed requiring the development of a repair strategy to address potential structural risks until replacement of the structure and to potentially reduce the rate of deterioration. This paper presents the development of the physical concrete properties over time, parameters to be used in and results of the structural analysis, future structural behaviour and a review of potential repair strategies.