2022 – Novel use of plastic concrete for coffer dam construction

Sasha Longo – Entura, Jamie Campbell – Entura, Neil Smith – Hydro Tasmania

There have been numerous documented uses of plastic concrete in cut-off walls around the world, but its use as the primary impermeable barrier for a coffer dam is limited. As part of the Tarraleah Hydropower Upgrade intake works at the Lake King William site in Tasmania, a plastic concrete core was chosen for the coffer dam due to its versatility. A plastic concrete core will create an effective seal if water is encountered in the foundation and can allow post construction grouting if leakage through the fractured rock foundation is deemed significant. Furthermore, the impermeable core can be constructed in any weather conditions, presenting significant benefits to the construction schedule compared to a clay core or liner options. A plastic concrete core is an appropriate choice where limited geotechnical information is available and the ability to undertaken post construction grouting at any water level is required. This paper explores the research, development and concrete trials of a plastic concrete mix, with strength between 1 and 3 MPa (28-day mean) for use as an impermeable core in a coffer dam.

The paper will provide the reader with additional data for specifying a plastic concrete cut-off and highlight the benefits and issues associated with utilising plastic concrete. Currently the design for a cut-off utilising the plastic concrete is underway with construction planned in late 2022.