IN NUMBERS THE ADVANCEMENT OF TUNNEL BORING MACHINES ACCIONA is one of the leading companies in the use of TBMs for infrastructure mega projects. Its R+D in geotechnics is helping to make them the safest and most efficient excavation technology. Having bored more than 800km of metro, railway and highway tunnels, the company is a leader in adapting and managing TBMs. It has participated in record-setting projects, including the Follo Line (Norway), the metro systems in Quito and Sao Paulo, the Legacy Way freeway tunnel in Australia and the tunneling of the M-30 in Madrid. • Some are among the largest in the world: 15 m in excavation diameter, 100 m long, (equivalent to a 5-story building) and weighing close to 2,800 tons, (approximately 15 Boeing 747 airplanes). • It uses several types of TBMs depending on the geology of the subsoil, whether or not water is present, the urban layout and the monitoring of settlements: single shield and double shield (protection for excavation operators from behind a cylindrical metal shield), hydro shield (in the excavation of soft materials where water is present) and earth pressure balance shields (like the hydro shield but in cohesive soils). • 20 people work in them at a time and up to 140 in shifts throughout the entire excavation process, including external logistics and support, 24 hours a day.