Central Highlands Water – Dams Condition Assessment, Ballarat, Victoria, Australia
Central Highlands Water
In 2000 to 2001 ATC Williams, then known as MPA Williams and Associates, completed a major investigation of the geotechnical condition of nine dams owned by Central Highlands Water, Victoria. The project was carried out with Hydro Tasmania and Sinclair Knight Merz.
The aims included work to:
- Investigate the existing condition of the dams.
- Assess the adequacy of the dams with respect to stability (including seismic loading), seepage and erosion/piping.
- Recommend remedial measures where required.
The dams were all earth or earth / rockfill construction. The largest, and most recent, was the 45m high Bungal dam which forms the Lal Lal storage. This dates from the late 1960’s, and in design, construction and documentation represents a “modern” dam. The other dams investigated were smaller, and much older. Some are thought to date back to the gold rush.
The common themes running through the investigation and assessment of these older dams are:
- Original construction pre-dated modern earth moving and compaction methods (probably horse-drawn equipment, or at best steam engines).
- Original design pre-dated modern soil mechanics (many of the dams have features which would not be considered good practice today) including embankments details such as puddle-clay or concrete core walls.
- Many dams have been altered, raised or constructed in several stages.
- Design and construction records are generally poor to non-existent.
- Instrumentation and monitoring data is limited.
The work commenced with a process which might be called “mining the archives”. This is a detailed review of available documentation to build up a picture of the structure. This was followed by a detailed walkover inspection, detailed geotechnical investigation and laboratory testing program. The dams were then analyzed for stability under both static and seismic conditions, with several requiring the design of additional structural elements, such as downstream berms, to adequately improve stability.
A comprehensive geotechnical investigation report was produced including ongoing monitoring for all dams, and recommendations for remedial measures to address issues such as seepage, erosion as well as stability on some dams.
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