Why tunnels work

Tunnelling is becoming a popular solution as cities around the world look to expand their transport networks. They are very useful in locations where aboveground options are exhausted and communities place a high value on land at ground level.

Tunnels allow for effective, secure train operations and offer a viable alternative to an aboveground rail system. They save space and reduce cost. They also minimise potential environmental impacts on existing residential and business areas, compared to aboveground options.

Construction of tunnels

The most significant construction site for the Forrestfield-Airport Link will be near the main tunnel portal at Forrestfield. This area houses the key infrastructure, including bentonite and slurry treatment plants, which support the tunnel boring machines. The site will eventually be home to a new train station and car parking facilities.

The tunnel boring machines were launched from this site in 2017 and are making their journey to Bayswater, constructing the tunnels along the way. The tunnels vary in depth along the route, with the deepest point being beneath the Swan River, where the roof of the tunnel will be approximately 26m below the riverbed. Overall, the depth of the tunnels average 15m below the surface.   

Cross passages (allowing access between the tunnels) and emergency exits will be constructed at various points along the rail route.

Experience in building tunnels

Salini Impregilo, part of the joint venture with NRW to build the Forrestfield-Airport Link, has 100 years’ experience building tunnels and infrastructure around the globe. Their work to date includes 6830km of railways, 400km of metro systems and 1450km of underground works. The company is experienced working in challenging environmental conditions, such as those found in Doha and Riyadh, where it has been involved in two of the biggest metro systems in the world.

Read more information about some of the company’s projects, either completed or underway.


The length of the TBMs


The number of pre-cast concrete segments