Engineers Australia

Diaphragm walls and cutter soil mixing

Russell Denny

Abstract

Diaphragm walls are a specialist foundation construction technique which has been used at all three rail receival dump stations and conveyor tunnels for the existing coal loading facilities on Kooragang Island. The subsurface soil profile at Kooragang Island comprises deep deposits of estuarine sands, silts and clays overlain with dredged sand fill, with basement rock at about 40 m depth and water table only 1 m to 2 m below surface. These conditions are suited to diaphragm wall techniques.

The diaphragm wall method was first used in the 1940’s and has steadily grown in use around the world. Despite being reasonably common in other parts of the world, this specialist technique was not often used in Australia. The occasional diaphragm wall projects that were required were generally done by offshore specialist contractors. Wagstaff Piling first gained experience in diaphragm wall construction in 1987 and became the only Australian owned foundation contractor to use the method. The Stage 2 expansion of the coal loader at Kooragang in 1995 was then challenging in that it was the largest diaphragm wall project we had embarked on. The Stage 3 expansion to the coal terminal in 2000 was a similar magnitude wall, but complicated by the close proximity of the rail loop, the Stage 2 expansion dump station and conveyor tunnel, as well as coal stackers and reclaimers operating during construction of works.

A 4th expansion to the coal loading terminal has commenced with diaphragm wall techniques likely to be used to construct the walls of the new dump station and conveyor tunnel.

This paper provides an overview of the diaphragm wall method used and discusses the new technique Cutter Soil Mixing (CSM), which has been introduced to Australia by Wagstaff Piling, and which can be used in similar conditions.