Bath structure
25 Nov 2014

Lower level structures work underway

The travelling public may have seen bridges being constructed for the Tonkin Highway / Leach Highway interchange but the Northern Zone team is also advancing the future interchange’s lower level structures.

One of the main types of lower lying structures for the interchange are concrete baths. These are special structures that provide a waterproof running surface for traffic where a road is constructed below ground water level. In the aerial image above the bath structure lies beneath one of the bridges of the future Tonkin Highway / Leach Highway interchange.

When the interchange was being designed, the team had several challenges to contend with, mainly the aviation height restrictions in place due to the interchange’s proximity to the Perth Airport runways. There was also a desire to implement a design with sustainability in mind which could lead to environmental and economic benefits arising. 

The design team looked at ways to make the three baths required at this interchange as shallow as possible. By implementing a shallow design, less dewatering would be required during construction of the interchange. Varied road geometry, a more efficient structural depth on bridges, and gaining approval from relevant authorities for partial penetration of aviation constraint surfaces allowed the design of these lower level structures to be achieved.

As a result, less water is being displaced during construction which is a desirable outcome of the design. Dewatering was also minimised during construction of a pump station which drains the bath structures by using a combination of a closed sheet piling cofferdam and deep dewatering wells. A cofferdam is a structure that retains water, allowing an enclosed area to be pumped out.

Work on the bath structures will continue until the end of the year. When opened, the Tonkin Highway / Leach Highway interchange will provide a major new access to the Perth Airport.