The Joberg tunnel: successful tunnelling in moraine
A 100 meter long tunnel in mixed face moraine and rock, below the ground water level, was the solution when the southern end of the Joberg tunnel had to be located in an area with high risk of rock fall. The rock fall risk from the steep mountain side was evaluated to be so high that an open cut was not an option. Since a rail tunnel in clay was constructed in Trondheim in 1942, using overpressure chambers, this is the first planned soil tunnel in Norway ever built. The soil tunnel has been successfully completed in May 2016 by using typical soft ground tunneling methods. The excavation required a good cooperation between contractor, client and designer at site. Tunnel face and profile stability have been maintained by a steel pipe umbrella and immediately applying sprayed concrete and installing additional spiles, anchors etc. as required. Water ingress have been controlled by using drainage pipes in the tunnel and pumping wells drilled from the terrain along the tunnel alignment. Deformations have been measured by convergence profiles in the tunnel and terrain, and an 30 meter horizontal inclinometer installed above the tunnel. Deformations in the tunnel have been within the range of 12-27mm.