Breaking new ground with the Brenner Base Tunnel21 October 2013
The Brenner Base Tunnel is pushing the boundaries of engineering innovation and environmental accountability. Christian Doherty talks to Raffaele Zurlo, the Italian CEO of BBT – the joint venture company delivering the tunnel – about the logistical and operational challenges of one of the world’s most ambitious construction projects.
The Brenner Base Tunnel (BBT)linking Innsbruck in Austria and Fortezza in Italy is currently one of the biggest construction projects in the world and marks the next evolution of Europe's tunnelling frontier. Running 55km (34 miles), the twin-tube tunnel begins in the Innsbruck suburb of Wilten and tunnels through the Alps, reaching a height of 840m (2,760ft) above sea level.
Conceived as a solution to the increasingly congested transport routes between northern and southern Europe, the railway tunnel will allow the smoother, faster transit of freight from the ports of Naples and south-eastern Europe to the markets of the north. It will also significantly increase passenger capacity on trains.
For Raffaele Zurlo, the Italian CEO of BBT, the joint venture company delivering the tunnel, the scale and complexity of the project is both a challenge and an opportunity to advance tunnelling science and engineering to the next level.
"The excavation methods used for the BBT include drill and blasting techniques and mechanised excavation," he says. "When blasting, special machines called jumbos are used to drill a certain number of holes in the rock face, which are then packed with explosives. These explosives are set off at the same time or with specific brief delays: this phase is known as a 'volley'. The position and the depth of the holes and the amount of explosive vary with the geomechanical characteristics of the rock mass to be excavated."
Zurlo explains that the choice of the most appropriate excavation method, whether it be mechanical or blasting, depends on multiple factors.
The most important is the physical parameters of the rock mass [such as hardness and alteration], the configuration and disposition of fracture planes and underground water conditions," he says. "And considering the tunnel system as a whole [main tubes, exploratory tunnel, lateral access tunnels, cross-tunnels, chambers], the Brenner Base Tunnel project requires around 44km of tunnels to be excavated using blasting and about 130km using a tunnel-boring machine (TBM), operating in parallel on several excavation fronts at the same time. So far, over 28km of tunnels have already been excavated, about 10.5km using a TBM."
Safety measures and engineering expertise
Clearly a project on such a mammoth scale requires not only engineering excellence, but also a constant focus on safety. The main risks centre around the extreme temperature and humidity conditions underground, the presence of particulate dust - the most dangerous being silicates - and harmful or explosive gases, and the possibility of rock falls from unfinished tunnel vaults, not to mention the risks associated with operating such powerful machinery and equipment.
Given that accidents in tunnel projects remain an ever-present risk, Zurlo has taken the lead on mandating a zero tolerance approach to health and safety.
"The measures and precautions taken to guarantee the physical welfare of the personnel include forced ventilation with special equipment to ensure a constant in-flow of fresh air, use of wet drilling systems [drills equipped with water injection for dust suppression and control], wetting down of spoil, installation of electronic sensors to detect harmful or explosive gases, adequate lighting of work areas and usage of personal protection devices," he says.
Naturally, expertise on projects like these is in short supply; engineers, designers and planners qualified to lead such a complex project don't grow on trees. Zurlo admits that he has had to cast the net wide in order to find sufficient engineers.
"The original planning team was formed in the early stages of the feasibility study and more people have gradually come on board as the complexity of the planning stages increased and construction began," he explains. "There are also synergies in place with the future managers of the railway infrastructure [Austrian Federal Railways (ÖBB) and Rete Ferroviaria Italiana (RFI)] involving cooperation and the availability of specially qualified personnel."
In addition to that, the consortium behind the BBT has also made concerted efforts to bring in new blood, offering opportunities to students and graduates interested in further in-depth study of topics within their chosen fields.
"We work with schools and universities to support graduate theses and company internships that can also lead to permanent employment," says Zurlo.
Clearly, the effort to complete the tunnels has had a unifying effect.
"As a further incentive for our personnel and to promote loyalty to the company, we have introduced a bonus system based on specific goals that are agreed with management and tailored to the employee's specific role," Zurlo explains. "In any case, you could say the greatest attraction for our employees is the sense of being part of a huge, ambitious project, and it inevitably grows on you."
Future-proofing and environmental benefits
But while the BBT will, once completed, represent the very latest construction and maintenance techniques, the fact is that even the best-planned and conceived projects often appear outdated in the ensuing years, as what constitutes 'cutting edge' advances apace. The Brenner Base Tunnel is planned for a service life of 200 years, demanding serious attention to future-proofing the project.
Zurlo explains that various technical and engineering measures have been taken to ensure the durability of the structure.
"As an example, in defining the dimensions for the reinforced and non-reinforced concrete for the final lining of the tunnels, appropriate partial safety coefficients are used for the resistance parameters that take into account to service life of the structure," he says.
"Also, using laboratory tests, we carry out analyses on various cement mixtures to identify the ones that prove more resistant to CO2 dispersal, as this is considered a fundamental parameter to ensure durability of reinforced concrete structures."
The result is a reduction of the number of interruptions to maintenance operations, and an increase in the efficiency and functionality of the structure.
While the central driver behind the BBT's conception was cutting journey times and congestion, the design also reflects a determination to promote environmental benefits by lowering carbon emissions and removing road traffic from sensitive, overworked Alpine roads, in particular the Brenner Pass, scene of some of Europe's longest traffic jams.
In 2010, as part of the environmental programme, BBT commissioned a study from the EURAC research institute on the CO2 emissions produced during the construction phases and subsequent operation of the infrastructure, in order to evaluate the sustainability of the project and its long-term effects in light of European policies on climate change management and energy sustainability.
Zurlo says that BBT intends to further evaluate the feasibility of energy-saving best practices and the minimisation of environmental impacts, and, where possible, implement these during the planning and construction phases of the project.
"We're talking about things like the use of 'green' cement mixtures containing reduced percentages of Portland cement; the use of conveyor belts instead of heavy wheeled vehicles to move construction materials; the reuse of spoil as aggregates for cement production and/or as filler for dams and backfills; the use of geothermal energy from the warm waters that flow out of the tunnel at temperatures up to 30°C; and, in future, the use of the exploratory tunnel to run underground high-voltage lines and fibre-optic cables," he says.
Clearly, no matter what benefits the tunnel is expected to deliver over the long term, engineers, planners and other authorities are determined to ensure its construction involves minimal damage and disruption. According to Zurlo, to avoid congestion of traffic arteries and to limit, as much as possible, any nuisance effect caused by the presence of the construction site, specific logistical measures are implemented to transport spoil and for supply purposes; for example, by building roads especially for the construction site and areas for loading and unloading along the highways and using properly screened-off conveyor belts.
It's not just the human effects that warrant attention. Every effort is made to keep any negative impact on natural resources and the environment to a minimum.
"So, for instance, the portal entrances are carefully embedded into the landscape and the spoil disposal sites are located near the lateral access tunnels," explains Zurlo. "New nesting and feeding points have been set up
for animals near the construction sites to reduce impact on the local fauna.
"For sensitive landscape types and potentially valuable archaeological sites, specific building site observers monitor any impacts on the environment and on natural resources."
As 2025 approaches, Zurlo and the BBT team are constantly re-examining and updating plans to make sure tunnelling remains on track. The chances of timely completion seem reasonably assured given the progress so far. Certainly there's little doubt that the meticulous approach adopted by Raffaele Zurlo and his engineers, one that has served the project so well, should continue to guide the tunnellers towards the light.