Benching is the process of removing the lower part of the tunnel to achieve the desired final height. Two surface miners were commissioned to assist this work. A surface miner has a large cutting drum and can cut about 50 centimetres deep as they travel along the tunnel floor. Roadheaders are also used to carry out benching using the large cutting boom on the front of the machine.
In sections of the tunnel where tunnel excavation and benching is complete, trenching is carried out. Trenching involves using a saw and hammer excavator to dig trenches for drainage infrastructure and electrical conduit.
Waterproof membrane is installed along the tunnel either as a plastic or as a spray lining.
A final layer of concrete is installed and smoothed to form a tunnel shell, ready for fit out with road pavement, panelling and electrical and mechanical equipment. The lining is sprayed on like shotcrete during the initial tunnel excavation phase.