The tunnel boring machines began drilling the rock of the Ekeberg hill halfway along the route, at Åsland, from where two double shield tunnellers have dug north towards Oslo and two others have drilled south towards Ski. Åsland was also where the facilities that served the keystone and concrete plants were located. The TBMs, with an excavation diameter of 9.96 metres, were designed to tackle the conditions they would face during excavation, such as high water pressures and strong rock resistance. The tunnel drilling project has also included the drilling and blasting of two caverns for the assembly of the tunnellers, 370 metre rescue tunnels connecting the caverns, an escape tunnel of 2.7 km in length, two transport tunnels of 427 and 394 metres in length, connecting the caverns and re?sub_confirmation=1 Website: http://www.acciona.com/ --Social Media-- Twitter: https://twitter.com/acciona_en Facebook: https://www.facebook.com/ACCIONA.English/ LinkedIn: http://acciona.sa/YsSOM Google +: http://acciona.sa/YsT6T Instagram: https://www.instagram.com/acciona/ Show more