Challenging Infrastructure Project Assisted by Monitoring and Numerical Modelling as the Follo Line Tunnels were Excavated Below Existing Tunnels

Abstract

Just south of Oslo Central Station, the new high-speed Follo Line railway tunnels pass beneath the existing Ekeberg road tunnels. This paper presents the construction methods, numerical model, and monitoring program used to assess the stability of the E6 road tunnels during the excavation of the Follo Line tunnels only a few metres below. The construction of the Follo Line was approved subject to three conditions: (1) there should be no negative effect on the stability of the Ekeberg tunnels, (2) the traffic flow in the Ekeberg tunnels had to be maintained at all times and (3) any risk of instability in the existing tunnels must be detected beforehand, so that necessary precautionary actions could be taken in good time. To deal with the challenges, SINTEF developed a comprehensive analysis procedure, combining continuous rock stress measurements and displacement measurements with 2D and 3D numerical modelling. The rock stress change monitoring was used together with the numerical model to monitor the stability conditions in the Ekeberg tunnels as the Follo Line tunnels were excavated. This ensured that any risk of instability in the existing tunnels could be detected in advance to enable precautionary action to be taken. The successful completion of the new tunnels without any disturbance to the road tunnels shows that the procedure would be useful for dealing with similar applications in the future.

Investigation, numerical model, and monitoring for Follo line - a metro project in Oslo

“… Early registered data from monitoring equipment can be used with the corresponding rock mass behaviour observed during the construction to design and test the warning system well before the construction progress to the critical area -under the Ekeberg tunnels. Description of the monitoring program and warning system can be found in Trinh et al [4] and [6]. The locations of the monitoring system are presented in Figure 8.…”

“…A possible explanation for this could be joint movement and better rock contact to increase the stress evolution. After the "no reading" period, data from the LTDMs became unreliable as pointed out in Trinh et al 2021 [6].…”

Influence of dynamic disturbed frequency on rock failure characteristics under triaxial cyclic and multistage unloading confining pressure loads

“…The rock mass in many engineering constructions, such as mining engineering, 1–4 petrol‐gas engineering, 5,6 hydropower engineering, 7,8 and road engineering, 9,10 is inevitably exposed to complicated stress disturbance conditions. The disturbed source of blast vibration, excavation, drilling, wheel loading, or natural earthquake is usually equivalent to cyclic or fatigue loads 11–14 .…”