Corrosion

A key feature of the Performing Arts Venue in north bridge, is the >100 year durability requirement – ideally the construction will service theatre goers for well past the century mark. Perth and Northbridge in particular, are built on reclaimed swampland between the river, and what is now – Lake Monger. Effectively, the lower half of this structure will be permanently submerged. Also during the  course of the geotechnical testing it became clear that there were pockets of acid sulphate soils in clays as shallow as 3.5m depth.

Sulfate ions tend to accumulate in coastal clays whenever ocean waters flood into an estuary. Such soils can react to form sulphuric acid if exposed to air, causing not only acidity and leaching of metals, but also a potential corrosion threat to building materials. Disturbing the soils can result in corrosion in surrounding buildings in addition to the environmental impact.

To contain all dewatering activities to within the boundary, diaphragm walls were erected to a designed depth to form a box, inside which, the water table levels could be controlled. The use of top-down construction and diaphragm walls eliminates the need for corrosion-susceptible permanent ground anchors to support the soil retention structure for the deep excavation.