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Alpine drive: Building the world's longest railway tunnel between Austria and Italy

Deep beneath the Austrian Alps a veritable labyrinth of tunnels and caverns is being created ahead of works to bore the world’s longest railway tunnel between Austria and Italy.

To us Brits, London’s £14.5bn Crossrail scheme is a mega-project pure and simple, with tunnelling machines about to start boring 21km of tunnels deep under London. But head to Innsbruck in Austria and they will laugh in your face, describing Crossrail as little more than a scratch.

Here, engineers are preparing to start construction proper of what will be the longest railway tunnel in the world - the 65km long Brenner Base Tunnel that will run up to 1.8km beneath the Alps. The project will halve travel time on the rail line between Munich and Verona and form a key link in the planned 2,200km long route from Berlin to Palermo on the Italian island of Sicily (see box).

In 2026 the tunnel system will run to a mindboggling 230km

It is important to stress “construction proper”, because ahead of the start of tunnelling for the twin bore running tunnels in 2016 a Crossrailesque amount of tunnels will have already been built.

Indeed, as of today, 20km of tunnel has already been blasted out as part of advance works that will create access to three tunnel boring machine (TBM) launch caverns, spoil disposal routes and, in an unusual move, an exploratory tunnel that will run the length of the route.

When all is said and done, in 2026 the total length of the tunnel system will run to a mindboggling 230km, with 8.1m internal diameter twin bore running tunnels 70m apart at its heart.

There will be a 5m minimum internal diameter exploratory tunnel nestled between and around 12m below them, access tunnels and cross passages. Factor in some extremely challenging geology, not least a sandy Periadriatic seam - a geological fault zone where the European and African tectonic plates collide and where water pressures are expected to reach 17bar - and it’s a pretty big test.

High stakes

It also comes with a pretty hefty price tag with a construction cost of €7.5bn (£6bn). Of this, 27% comes from the European Union and the rest is shared equally by the Austrian and Italian governments. The project is being run by project promoter Brenner Basistunnel (BBT), a 50/50 joint venture between the Austrian and Italian governments.

On the Austrian side all responsibility lies with state rail operator OBB. On the Italian side it is slightly more complex, with a delivery body set up to run things. This body is 83% owned by Italian state railway company RFI but the three local authorities that could be most affected by the works hold small stakes.

This is primarily to ensure environmental concerns are tackled at the highest level and goes some way to explain the project’s long gestation period.

Deciding to press ahead has not been quick or easy, with the project first mooted in the post Second World War transport boom of the 1950s. Even back then it was clear that extra capacity was needed: the existing 1860s-built rail route over the Brenner Pass is tortuously slow with tight curves and steep gradients of up to 31% seriously restricting capacity. To this day, three locomo tives are needed on every freight train - two at the front to pull the train up the mountain and one at the back to control it on the way down. But despite the obvious shortcomings of the route, little happened beyond the drawing up of some ambitious sketches.

“It is not a high speed route, it is a high capacity route. In Austria, high speed is a ghost you don’t mention.”

Meanwhile demand continued to rise - the Brenner Pass is used for 40% of all freight traffic crossing the Alps - and with no way of increasing rail capacity, road traffic has grown and grown on the parallel motorway route, leading to frequent traffic jams.

“For us, it is more an environmental project. More than 50M.t of freight crosses the Brenner pass a year, 35M.t of which is by road. We want to shift the freight from road to rail,” explains BBT head of communications Simon Lochmann.

“It is not a high speed route, it is a high capacity route,” he adds. “In Austria, high speed is a ghost you don’t mention. We’re not France, unfortunately.” While design speeds are 250km/h for passenger services and 160km/h for freight, actual speeds will be limited to 150km/h. “But even at 150km/h that will make such a difference to the 40km/h speeds we get now,” he adds.

A serious study completed in 1989 nailed down the current route from more than 80 options. In 1999 the project promoter BBT was formed and work got serious.

First, to clarify. What is being described as the Brenner Base Tunnel is actually two separate tunnels. A 9km single bore, twin track bypass of the city of Innsbruck was built in 1994. This will get a parallel bore created as part of this project to be used as a rescue tunnel. New, tunnelled, connections will connect this link directly to the 55km tunnel beneath the Alps which is now in the early stages of being constructed, making a tunnel 64km long overall.

Two bored tunnels will make up the running tunnels on the project proper, but before BBT even thinks of tendering for that work it is cracking on with its exploratory tunnel.

Saving costs

This is designed to provide a wealth of geological data that will allow it to better inform tenderers. “We are confident we will save time and money on the main works through a better understanding of the geology and water pressures,” says Lochmann. “It gives us more security that our proposed construction methods are the right ones, so we will know how to tender the main lots.

“We are quite sure it will save us money - even though it is costing us £725M to £800M to build,” he says, adding that current fiscal woes mean that both governments are already demanding savings.

The exploratory tunnel is not just for exploration, however. In use, it will act as a drain for the main running tunnels and will provide service access. But it will not be used in the case of emergency evacuation. For that, cross-passages will be built linking the running tunnels every 330m.

Brenner_tunnel

Construction of the exploratory tunnel began in September 2007 and work will carry on until April 2014, according to the latest schedule. So far, approaching 15km has been excavated, 10.5km by tunnel boring machine (TBM) through granite from the Italian portal at Aicha and 3.7km from the Innsbruck end.

From both ends it has been steady going on slow progress. “The TBM has progressed at between 10m to 25m per day, but it is more 10m than 25m,” says Lochmann. At the northern, Austrian end, excavation has been by drill and blast through very poor ground of mainly quartz - work that has proved the worth of the exploratory tunnel principle.

“Because the ground was quartz we didn’t think a TBM would work,” says Lochmann. “But now, having done it, we know we could use a TBM.”

Work on the exploratory tunnel has just entered its most complex phase, with the fi rst volley of blasting for the excavation through the Periadriatic fault. This is on the Italian side and picks up where the TBM left off . In the next two years a further 1.3km of tunnel along with a 595m long TBM assembly cavern will be excavated by drill and blast through sandy ground where water ingress of 150l/s is expected. So far around 200m of tunnel and 200m of cavern has been excavated by Consorzio Brennero 2011, a contracting joint venture of Italian firms PAC, Cogeis and Oberosler and Austrian firm Implenia in a €53M (£43M) deal that also included construction of the 1.8km long Mauls access tunnel.

“This will be become the biggest construction site on the tunnel and 15 years of construction traffic is just not acceptable”

Work on the four access tunnels is well advanced. Near the Italian border on the Austrian side the 4km long Wolf access tunnel is also well underway, with 400m complete when NCE visited in March. But importantly two other associated tunnels are complete at the Wolf site. One is the 700m long Padaster tunnel that will be used to convey spoil to the 1.5km long, 300m wide valley that has been earmarked as the dumping ground for material removed by TBMs operating from Wolf. The other is the 1km long, 10m diameter Saxen tunnel that will give site traffi c direct access to the motorway network.

Traffic congestion

Material is being dumped locally to minimise lorry movements, and what lorry movements there are will not impact at all on the local infrastructure with the work sites linked directly to the motorway network via purpose built link roads and tunnels.

“The access tunnels connect to the motorway so that no lorries pass through the villages. “This will be become the biggest construction site on the tunnel and 15 years of construction traffic is just not acceptable,” stresses BBT Wolf site project manager Andrea Lussu.

“The traffic levels here are already high so we want to produce as little as possible,” adds Wolfmann.

“At our peak there will be one truck every two minutes. Having them on local roads is not an alternative.”

Back in Innsbruck, excavation in the 1.3km Ampass tunnel that will provide access for TBMs is now underway. This will create the rescue bore for the Innsbruck bypass tunnel.

Most impressive though is the 2.4km long Ahrental access tunnel, 5km from Innsbruck. There, contractors have excavated 1.7km of the 2.4km long route, at a 1 in 10 downward incline. It’s another 700m to the point of intersection with the exploratory tunnel, which has already reached that point. But at a rate of 5m/day, it’s going to be the end of the year before there is another breakthrough to celebrate.

“We have 700m still to go,” notes Christian Nemec, BBT project manager for the Innsbruck end exploratory tunnel and Ahrental access tunnel.

All access tunnels are being constructed by drill and blast with a sprayed concrete lining applied in two layers. The primary layer is a hefty 200mm to 400mm thick; after that a reinforcement layer is erected, held in place by rock anchors at 4m centres and fi nal 100mm thick sprayed concrete layer will then be applied.

Top secret mix

Austrian standards and local site conditions demand a pretty special concrete, and the mix used owes much to materials science knowledge gleaned from the UK.

Materials giant Hanson’s Ketton quarry in the East Midlands has been providing a fantastic cement for sprayed concrete to UK projects like the Hindhead tunnel for many years.

Hanson’s German parent Heidelberg Cement has learned from this, creating a top secret mix for Brenner from Austrian cement that still generates the early strength development demanded by tough Austrian design codes.

It also provides the sulphate resistance demanded by the local site conditions (see box).

“We needed sulphate resistance - so we used a special cement,” says Heidelberg Cement technology centre senior scientist Martina Dietermann. Heidelberg is supplying the Wolf and the Ahrental tunnels.

A mock up in Heidelberg’s lab back in Germany proved the mix was up to the task. “The complication in developing materials like this is that you have to have a way of measuring the strength as the concrete cures. We do this first in the lab,” says Dietermann.

Insitu it is also tested every 200m, with independent strength tests carried out on every 2,000m3 applied. “So far it has all passed the test,” she says.

It’s not just the concrete that is getting regularly screened. Since 2001 the project team has installed more than 1,350 water quality monitoring points to ensure that the construction activity is not interfering with the hundreds of vital private wells and boreholes that supply farms and villages across the Alps.

“We have 10 to 15 diff erent sources lined up in case we do interrupt supplies,” explains Wolfmann. “It is quite an important issue for every mayor in the territory.”

“This is not just a tunnel project at all. It is water engineering, power engineering, you name it”

The monitoring is a serious business and one that takes place come rain, wind, sleet or snow. “These locations are remote and we have water measurers carrying out daily checks by skis,” he adds.

It’s not just water that is being monitored. Being the Alps, avalanches are a real threat, especially when you are blasting away at the mountain.

“A team of 15 people comes in once a week to check that we are not doing anything to trigger avalanches,” says Lussu.

Air monitoring is also intense, with several air monitoring points at each work site linked directly to the offices of environmental control officers in Innsbruck.

The team has also had to move and rebuild a reservoir and hydropower plant and is right now in the process of diverting a river that runs along the bottom of the valley to make room for a spoil dump. The environment comes first in Austria.

“Right now we are spending £16M building things just for environmental requirements,” adds Lussu. “This is not just a tunnel project at all. It is water engineering, power engineering, you name it. It makes the work really interesting.”

Keeping the locals on board is also an important part of this phase of works, and community engagement is taken seriously. “Every week we deliver an update to all residents,” explains Lussu. And this is no email update. “We deliver it by hand,” he says. “It means we drink coff ee with them - even schnapps - because it’s important. Face to face is better.

The community engagement goes further, with contractors compelled to house site staff in rented rooms rather than on static caravan compounds.

“This is not a wealthy area these days and it means the locals are getting something out of the project,” says Lussu.

Starting work

The construction phase proper officially began on 18 April last year with an official signing ceremony, but no actual construction contracts have been signed - the project is still assessing the data yielded by construction of the exploratory tunnel. Main contracts are expected to be let in 2016, and work is likely to progress with six TBMS operating simultaneously.

Wolfmann is confident nothing will stop this happening. “The last year has been very significant. We have six construction sites operating. It is now very hard to stop this project,” he says.

 

Berlin to palermo


Even at £4.8bn the Brenner Base Tunnel is a small part of a very ambitious plan to create a largely four-tracked, capacity-enhancing railway from Berlin to Palermo.

It is a bold plan, but one that is close to being realised. Of the 2,200km route, around 50% is already in operation, 25% is under construction and 25% is in planning. At the northern, German, end, 20 tunnels are currently under construction.

In Italy, the hard part between Bologna and Florence has been built. The Brenner Base Tunnel is part of the 425km long Brenner
line between Munich and Verona.

 

 

Cement innovation

brenner_tunnel_Spritzen_4346

Heidelberg Cement and Hanson have over 30 years of experience in developing concrete mixes for tunnelling projects worldwide. Hanson UK has developed technical and product capability that has been proven in tunnelling projects throughout the UK; and this technical expertise is now being used across Europe.

Its Ketton plant in the East Midlands manufactures a unique and stable cement that is proving very effective when used in sprayed concrete tunnel linings. Its much lower “bounce-back” cuts waste and saves time.

The firm is understandably tight-lipped about what makes its cement so special, but it is applying knowledge gleaned from this to cement mixes at Brenner. “Besides the high sulphate resistance we don’t want to publish in detail what makes our cements special,” says Dietermann. “But what we can say is that the reactivity of the cement has been specially optimised for sprayed concrete by optimising the cement composition.

Application

“The application method, the spraying, requires very high early strength. To reach this an accelerator is added at the nozzle of the mobile spraying unit. For health and safety reasons a nonalkaline accelerator is used. The effectiveness of this depends significantly on the cement used.”

Since the accelerator is the most expensive component of the mix besides the cement, dosage usually is limited. Not here. “High early strength cannot be reached with every cement in a cost effective way,” says Dietermann. “This situation demanded an optimised cement.”

At Brenner the onerous specification is for a C30/37 strength sprayed concrete, capable of handling exposure classes XC4 for cyclic wet and dry conditions and XF1 for handling moderate water saturation without de-icing agents. In certain sections additionally XA2 standards for coping with moderately aggressive chemical environment, must be met.

In addition it was required to fulfil meet the J2 early strength class for sprayed concrete as defined by the Austrian Society for Concrete and Construction Technology. J2 strength is deemed necessary if sprayed concrete is to be placed in thick layers at a high delivery rate. It is also demanded in locations with water seepage (Brenner has plenty of that) and when it needs to withstand immediate loading due to subsequent operations such as the drilling of anchor holes or where vibrations are caused by blasting. J2 strengths also have to be achieved where there is rapid load build-up due to rock pressure, earth pressure or gravity loads.

Super high strength

Hanson’s concrete meets this and even eventually cures to J3 strength - a super-high strength that is only usually specified under special circumstances where there is strong ingress of water, where there are load-bearing requirements, or where there is a very fast rate of advance. It is not usually specified because the high cement content demanded means that application generates a lot of dust and bounceback is high.

Hanson’s special mix minimises this - and the amount of accelerator is evidence of this, with 6% by weight added as a rule, rising to 7.5% when the sulphate resistant cement is used.

 

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