Stockholm International Airport, Sweden. 1995-1997.

Construction of underground terminals at Arlanda Airport and the 50km fast link to Stockholm Central Station (Arlandabanan). Tunnel & GeoConsult was NCC and Arlandabanan's chief geologist during the construction period. The underground intercity train station (600 meter long) under the international terminal and the trainstation under the domestic terminal 2 including shafts with lifts and escalators to the terminals.

 

 

Figure: The 600 meter long Intercity train station. Cavern span 23 meter. Geology: micaschist.

 

The Arlanda Link project. Construction of underground railroad tunnels and 3 terminals under Arlanda International airport started July -95 with the rock works finalized 2 years later in October -97. Contractor was swedish NCC and SIAB in a joint BOT project named "Banbrytarna". The fast rail link connects Stockholm central station to the airport with a travel time of less than 20 minutes. The high speed connection was opened for traffic in October -98. The total amount of rock excavated was 800.000 m3 with 8 km of tunnels including 3 subway stations. High horizontal stress due to low rock cover under critical terminal buildings (down to 10 meters) the excavation was closely monitored with convergence and extensometer instruments, plus vibration monitoring. Preinvestigations had shown relatively high horizontal stress levels (>10Mpa) which gave the surpricing results that hardly any settlements were observed but a heave of up to 10mm occured on the surface above the larger caverns right after excavation. This had no negative impact on existing buildings and thus the initial rock stress increased the stability of the critical area around the Arlanda terminals and no extra rock support were needed apart from normal rock bolts and shotcrete.  Strong restrictions on the ground water table made it neccesary to include an extensive and systematic grouting process. The geology consisted of massive granodiorite and softer micaschist.   Tunnel & GeoConsult was NCC's chief geologist during the 2 year construction period. The geoengineering department consisted of 4 geoengineers and one Cad operator handling at peak periods 16 construction faces.