Harris Dam Slurry Trench: Slurry mix design

The Water Authority of Western Australia has recently constructed a dam across the Harris River, 10 km north of Collie, a town in the south west of Western Australia. The dam is an earthfill type structure, 35 m high and 430 m long. The dam is founded on in situ soils, approximately 20m to 30m thick, overlying predominately granitic bedrock.

The design of the dam needed to address problems associated with the predicted large settlements of the structure (in the order of 500 mm), and also problems associated with possible seepage through the foundation soils with permeabilities of the order of 10^-5 m/s.

The chosen solution to reduce the seepage through the foundation soils was the construction of a cement-bentonite slurry trench cut-off. The cut-off trench was supplemented by a grout curtain to minimise seepage through joints and fractures in the underlying bedrock.

The rationale behind the selection of a slurry trench cut-off as the means of reducing seepage through the foundation soils, as well as construction aspects, are discussed in the accompanying paper (1).

The process of designing a slurry mix capable of fulfilling the design and construction criteria is discussed in this paper.