To build the Lower Plenty Road and Manningham Road interchanges, we’ll be using a tunnelling method called cut and cover.

Massive concrete walls will first be built deep into the ground. These walls are known as diaphragm walls (D-walls).

The soil will then be removed from the ground and a large horizontal concrete slab will then be poured to make the tunnel roof. Once the roof is in place, surface work can resume as construction works continue below.

As part of this construction method, we will need 65,000 tonnes of a naturally occurring clay to help build the tunnel wall structures.

The clay is mixed on site and pumped into the excavated holes that will eventually form the walls for the interchange. It keeps the soil stable before we fill the hole with concrete as we form the walls underground. We then pump the clay back out, filter it and re-use it in the next dig.

Purpose-built clay manufacturing plants have been built at our Lower Plenty Road, Manningham and Trinity sites, where cut and cover works are underway.