An overriding theme that runs through this month’s T&TI is one of dealing with the unexpected. This is clearly illustrated in the focus on ‘Central Europe’, which offers four site reports from four completely different types of tunnel project. Although each describes projects, either built or still under construction, using very different methodology, they all have one thing in common – things haven’t gone according to plan.
At the Egge railway tunnel project in Germany, the team’s NATM design was tested to the limit when the geology proved far more troublesome than expected. Also in Germany, the Herren twin bore road tunnel, under the River Trave, experienced an extremely problematic first TBM drive, which led to modifications on both the machine and separation plant. These modifications saw production increase by more than 60% on the second bore!
In Switzerland, a whole team was pushed to its limits during the construction of the Oenzberg rail tunnel. Coping with either a ground collapse, a bearing failure, or an under-spec separation plant would alone make life very difficult, but this project had all three – and still came in on time! Finally, on Switzerland’s famous 57km long Gotthard Base Tunnel, timely completion of the Faido Multifunctional Station (MFS) is critical to the project’s success. Following a collapse whilst drill and blasting the area’s construction cross cavern, it was discovered that the MFS’ northern tunnel branch (and widest cross-section) sat right over a major unforeseen fault zone. This has led to the team at Gotthard considering a complete shift of the entire MFS towards either the north or south.
The key is in how the various team members, from contractor to consultant, and in some cases even the client, pool together their knowledge and resources to overcome some severely testing situations. A flexible approach and the ability to respond quickly to unforeseen events is a tunneller’s pre-requisite, and these skills have been shown in abundance on many of our featured projects this month.
As they say, ‘to every rule there’s an exception’, and T&TI certainly follows suit here. Far from a case of dealing with the unprepared, the gripping account of the fire that took place during construction of the A86 road tunnel in Paris, is a perfect example of careful planning and safeguarding! The extensive fire mitigation measures put in place by the entire project team before construction commenced, almost certainly turned a potential disaster into triumph for construction safety, and should be held up as an example to all.
Tris Thomas
