Catagunya Dam restoration project
Client: Hydro Tasmania
Location: Tasmania, Australia
Date: June 2000 – August 2010
Investigating dam stability and designing a cost-effective upgrade solution for long-term dam safety
Background
Catagunya Dam is located on the Derwent River in south-east Tasmania. Designed in the late 1950s and completed in 1962, Catagunya is a 49m-high concrete gravity dam that relies on a large number of 200t-capacity post-tensioned steel cables to provide the necessary structural stability. These old style anchors are protected against corrosion only by the grout column. A 1999 risk assessment highlighted safety deficiencies at Catagunya Dam due to the unknown integrity of its post-tensioned anchors.
Solution
Rather than abandon all these anchors, Entura developed an investigation program to assess the integrity of the anchors. The investigation and assessment undertaken at Catagunya Dam indicated the likelihood that some corrosion of the anchors was occurring and that the integrity of the original anchors could no longer be assured. As a result, a decision was made in 2004 to cease reliance on the anchors, and in 2009-10 major upgrade works occurred. The stability of the dam was restored using 92 modern, large-diameter and corrosion-protected post-tensioned anchors that can be monitored for their load.
At Catagunya Dam, tensile steel reinforcing is required on the top surface of the downstream face of the spillway to support the large cantilever overhanging the spillway. This steel was to be severed as the large-diameter headblocks for the new anchors were cored. A major innovation for this project was the use of carbon fibre reinforcement to provide this tensile capacity.
Outcome
Detailed investigations including in situ groundwater testing, laboratory corrosion testing, in situ potentiostatic polarisation testing and detailed analysis concluded that the old anchors could not be relied upon, and therefore provided a strong case for these major upgrade works. The most cost-effective solution to stabilise the dam was to install new modern, very high capacity, post-tensioned anchors, which are now monitored on a 5-yearly basis. The restoration works were designed and constructed to maintain the hydraulic performance of the ogee crest spillway.
