2013 – Case studies of foundation grouting using the GIN method at the enlarged Cotter Dam

Sean Ladiges, James Willey, Matthew Norbert and Andrew Barclay

The Enlarged Cotter Dam (ECD) Project, located in ACT, consisted of the construction of a new 87 m high roller-compacted concrete (RCC) dam and two central core zoned earth and rockfill saddle dams up to 23 m high on the low points of a ridge to the south-west of the Main Dam. The Main Dam is the highest RCC dam constructed in Australia.
A continuous single-line grout curtain with a total length of 1.2 km was constructed across the full extent of the Main Dam and the two saddle dams with the aim of reducing future seepage losses through the dam foundations. The grouting processes were similar for the main and saddle dams respectively, however the grouting of the Main Dam and saddle dams was carried out as two separate contract packages by different subcontractors. As such, the project provides a unique opportunity to undertake a comparison of the foundation conditions and control equipment and outcomes from the two packages of work. The foundation conditions were different at each of the three dams, with varying geology across the site.
The saddle dam grouting was completed in 2010, with the grouting carried out at the base of the core trench prior to construction of the embankments, while the grouting of the Main Dam was conducted in 2012-13, with most of the grouting works executed from the drainage gallery within the constructed dam.
Consistent throughout construction of the ECD grout curtain was a similar philosophy of real-time computer control, the use of Grout Intensity Number (GIN) parameters, water pressure testing, desirable grout mix properties and the avoidance of damage to the foundations. There were a number of key differences in the grouting process for the saddle dams and Main Dam; these include the ground conditions, the pumping control systems used, the GIN parameters adopted and the grout materials and mixes selected.
This paper provides a critical evaluation of the two grouting programmes, an assessment of the effectiveness of the grouting, comments on tools and methods used, and proposes a set of recommendations for curtain grouting over a range of ground conditions based on lessons learnt during the project.

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