To ensure continued operation of the airport and the safety of tunnel construction as little as 4.5m below the operational airfield, the MultiMode™ Tunnel Boring Machine (TBM) was developed in collaboration with TBM manufacturer Herrenknecht and specialist pump supplier Putzmeister.

The machine uses compressed air face support with a novel piston displacement pump to maintain the seal. The MultiMode™ TBM provided successful delivery of the works, with negligible disruption to surface structures. In addition, all of the spoil from the tunnel could be reused in the earthworks on site.