ACCIONA has achieved the highest design score ever awarded by the Infrastructure Sustainability Council in its sustainability rating program in Australia. The NSW Government’s Western Harbour Tunnel (WHT) project in Sydney received a final score of 101.1 out of 110 and a “Leading” rating in the IS v1.2 Design Rating, positioning the project as an international benchmark in sustainable infrastructure.

This recognition reflects the integration of advanced environmental criteria across all phases of the project, from planning to design and construction.

One of the many achievements contributing to this design rating is a 42% reduction in potable water use, representing an estimated saving of 2,560 megalitres — equivalent to 1,024 Olympic-size swimming pools — over the project’s design life. Significant reductions in carbon emissions have also been achieved.

As part of their operation, tunnel boring machine (TBM) excavation requires the use of fluids that stabilise the ground and enable the extraction of material, generating slurry that must be properly managed. At WHT, the project is pioneering the innovative installation of one of the world’s largest underground slurry treatment plants. These facilities are usually located on the surface, requiring large areas and extensive pipeline networks to transport the material.

This solution eliminates kilometres of steel piping, reduces the number of slurry pumps and decreases heavy vehicle traffic on local roads. It also optimises water use, reduces equipment wear and minimises downtime.

The combination of these technical solutions and the project’s high design rating shows that the WHT exceeds sustainability and innovation standards for infrastructure.

The 6.5 kilometre tunnel, will be the first new road crossing of Sydney Harbour in more than 30 years. ACCIONA is delivering Stage 2, which includes the excavation of 4.8 kilometres of underground traffic tunnels from below the suburb of Birchgrove, on the western shore, to Cammeray, on the northern side of the harbour.

The use of an underground slurry treatment plant represents a key step forward in tunnel construction, significantly improving the safety, efficiency and precision of the works, while notably reducing impacts on the surrounding environment and communities.