The northern tunnel section of the E4 Stockholm Bypass will be 1.8 kilometres long and run under the Järva field, north of Hjulsta. We are undertaking extensive reinforcement and sealing of the rock here, as we have encountered challenges with the penetration of more water than expected.
One natural element of the work process when blasting and building tunnels is to make adjustments according to variations in the rock. Before we start working with the rock, we conduct preliminary studies and produce forecasts of the rock’s formation. There are always some uncertainty factors outstanding, as it is usually impossible to know in detail what it looks like underground.
Our ongoing checks revealed water penetration
We conduct our ongoing surveys of the rock when we blast the path of the tunnel in order to check its quality. The more we work with the tunnel, the more knowledge we acquire about the rock. This helps us adapt our work method to the natural variation and the uncertainties that can arise. However, our initial forecasts differ in some areas from the conditions exhibited by the rock. It was evident in autumn 2018 that there is more water penetration than we expected. So the rock needs to be reinforced and sealed more extensively than we originally planned.
We are slowing down to find the right sealing technology
In spring 2019, we decided to partly slow down the pace in order to analyse conditions and technical solutions to blast the path of the tunnel. This means that the work has taken a little longer than planned. On parts of the section, however, work has continued as usual with the goal of being able to continue safely and securely with production on a broad front.
Work is under way again
We are now under way again and have started blasting work on the sub-sections where we consider it possible, once we had found new ways to inject, seal the rock and check water penetration more carefully:
“On the sections that were put on hold earlier, we’ve evaluated the execution and upgraded the technical solutions. Among other things, we tested other means of sealing the rock, we’ve also sealed more, conducted water loss measurements and carried out more checks. We’ve now decided to proceed slowly with increased checking,” says Niclas Lindqvist, project manager for Tunnel North.