The Brenner Base Tunnel: A European Core Project
Tunneling is a worldwide business with often-changing markets. At the moment, everybody is watching the markets in Asia and in particular various huge projects in China and India, as well as the Middle East. With these busy hot spots, it’s easy to overlook projects elsewhere.
In this blog, I want to refocus and take a look at Europe, where there are some very interesting and challenging mega-projects underway for the Trans-European Network for Transport (TEN-T) of the European Union. The TEN-T connects all economies in the European Member Countries from West to East and North to South (Figure 1). This master plan for connectivity in Europe includes nine core network corridors with several projects crossing the borders of multiple European countries. The cross-border project implementation is complicated because of the different technical, financial and statutory requirements.
TEN-T core network projects
The core projects of the TEN-T master plan all serve as missing links that would connect the European Member Countries, like the Koralm and Semmering Railway Tunnels (both in Austria), Lyon-Turin Railway Project (connecting France and Italy), Fehmarn Belt Crossing (connecting Denmark and Germany), Brenner Base Tunnel (connecting Austria and Italy), Ceneri Base Tunnel (connecting Switzerland and Italy) and also some completed projects like the Oresund Bridge, Tunnel Road and Rail Fixed Link (connecting Sweden and Denmark), Milano-Roma-Napoli Railway (Italy), Gotthard and Lötschberg Base Tunnels (Switzerland), Betuwelijn Railroad (connecting the Netherlands and Germany) and the Channel Tunnel (connecting United Kingdom and France).
Financial support from the European Union in an amount estimated at 500 billion euro is required to complete this Trans-European Network and to widen some of the bottlenecks within it. The Brenner Base Tunnel is one of the most interesting cross-border projects and a core project of the TEN-T master plan (Figure 2).
Brenner Tunnel Conversations
The Brenner Base Tunnel (BBT) is a big challenge for all involved parties. In 2015, I had the great opportunity to interview Prof. Konrad Bergmeister, who has been the CEO of the BBT SE since August 2006 (Figure 3). Bergmeister was previously the technical director and head engineer of the company managing the Brenner Highway and was responsible for the planning and construction of new infrastructure and for maintenance of the existing structures. For the past 22 years, he has taught construction engineering at the University of Natural Resources and Applied Life Sciences in Vienna (Austria). He has been the President of the Free University in Bolzano (Italy) since 2010.
Interview with Prof. Bergmeister
Could you give me a brief overview of the Brenner Base Tunnel?
The Brenner Base Tunnel is a ground-breaking engineering project for the 21st century. This underground structure has a total length of 64 km and consists of three tubes: the exploratory tunnel and two main tubes with four lateral access tunnels connecting them together (Figure 4). The tunnel itself will become the longest railway tunnel in the world once complete.
The history of the tunnel is a long one: 160 years ago, an Italian engineer came up with the idea to go beneath the Brenner Pass. After World War Two, the project was reassessed but never proceeded. Finally, between 1987 and 1989 a feasibility study was carried out. The preliminary project was approved in 2002, and between 2005 and 2008 project details were worked out. In 2009 the environmental and technical approvals were obtained in Austria and in Italy. So we started with the first exploration of the whole rock situation in 2006, drilling vertical bore holes that totalled more than 28 km when we sum it all up. And this preliminary information was used in order to study the final layout of the tunnel in order to do the definitive design.
What, for an engineer, is the most challenging aspect of the Brenner Base Tunnel?
The most challenging issues for me are the following:
First of all we developed the so-called design guide in order to have the right basis to execute the design in both countries. This design guide was based on some new design ideas taking into account all the safety issues that have been proposed with the Eurocodes on a European level.
Second we developed internally a so-called chance and risk analysis, which should allow us to monitor the development of the project in terms of possible chances and risks. How we are doing that? Well we are trying to evaluate and double check the actual ongoing construction with our project managers and external experts and we are trying to identify all the possible risks and chances that might occur as tunneling proceeds. This analysis is part of a database that will be actualized on a yearly basis so we have additional information in terms of possible risks, additional costs, cost savings and scheduling.
The third issue is something that deals with some novel forecast technologies. We are using digital mapping and photogrammetric mapping as forecasting methods, particularly for the ongoing drill and blast operations. This is called the Tunnel Control System and is able to predict complex excavation shapes by using statistics regression analysis. It is based on 3D point clouds of the rock surfaces captured after each excavation, and the precision of previous excavated profiles is also analysed. The previous blasting data and the corresponding geological information are used for the prediction of the upcoming upper and lower blast profiles. For the forecast a certain number (minimum five previous blasts) is taken into account for a linear or nonlinear regression analysis. Through this optimization procedure up to 65% reduction in over-break has been achieved.
And the last issue is actually that we have been trying to develop ideas for the reuse of excavation material. The concrete mixture must be sustainable for the next 200 years since this is the lifetime of the tunnel. We have been studying the material of the exploratory tunnel (Figure 6), especially the schists, in the central zone of the project and we were able to modify the preparation methodology and optimize the concrete mixture to re-utilize 100% of the excavation material. Five years ago, all of the geologists and specialists during the approval phase told us that the excavation material must be disposed of. So this is actually a real step forward into optimizing the project excavation.
What is your opinion about the on-site TBM assembly of Robbins compared with the re-assembly of factory-built machines on jobsites?
From an engineering point of view we are only interested that the machine works very well on site. So we are interested to see, when the machine really starts, the performance in a certain excavation length. We are interested in the results and not so much on the specific assembly situation. There are different trade-offs: On the one hand, if you pre-assemble the machine in the production facility, this can guarantee you certain tolerances and probably certain pre-operation errors can be adjusted and finally avoided. But, the major problem is that you have to transport the semi-assembled machine on site and you have to re-assemble the machine on site again and then you have to start excavation. However, with Robbins for example, they can bring all the individual pieces on site and very often they are adjusting the machine itself directly under site conditions. It is easier, I think, to do the adjustment on site directly for specific logistics reasons. We can say that you might have more flexibility if you assemble directly on site compared with doing the assembly at the production facility.