Abstract:
The Stockholm Bypass is one of the largest rock-tunneling projects ever undertaken in Swedish history. The project consists of two main tunnels for road traffic, connecting the southern parts and northern parts of Stockholm with the aim to relieve the inner city of traffic. The northern part of the project (north of Lake Mä laren) has proved to have a geology that is far more fractured and conductive than what could have been anticipated based on early investigations. This has led to an ingress of water to the tunnels far higher than what the Swedish Environmental Court previously had allowed. The water ingress has resulted in the settling of – and consequently damage to – infrastructure in a vast area, calling for drastic measures to be taken to limit the water ingress in the tunnels. To deal with the high ingress of water to the tunnels, a new post-grouting concept was developed and ultimately initiated during the autumn of 2019. One of the main purposes of the design was to arrange the grouting holes in various geometries based on the prevailing geological structures, to obtain a higher probability of intersecting structures that could have been missed by the holes of the pre-grouting fans. The follow-up works of the new design has shown the difficulties of succeeding with post grouting. The main difficulties/uncertainties include: water ingress measurements, grouting hole geometries, geology, rheology of the grout mix and execution of the grouting. This text will focus on the follow up works and will present and discuss the difficulties and uncertainties related to a large-scale post grouting operation in a tunneling project such as the Stockholm Bypass.