High standards on Heathrow's ART

This article describes a complex tunnel project at UK’s Heathrow Airport that required tunneling over the existing Heathrow Express (HEX) line and under sensitive airport areas and services such as taxiways and fuel mains. A closed face tunnel boring machine (TBM) that could work in both earth pressure balance (EPB) mode and compressed air mode was used, allowing for flexibility in case settlement became extensive or granular material was encountered. The article provides an overview of the tunneling method used, settlement control methods, and tailskin grout injection. The twin 1.4km long Airside Road Tunnels (ART) will provide a new route for passengers and internal airport traffic traveling from Terminal 3 to Terminal 5.