Tunnelling: Big projects get bigger

Europe set the tunnelling pace this summer as first high speed trains ran through the 57km long AlpTransit Gotthard base tunnel, in Switzerland, the world’s longest transport tunnel, and the deepest at 2,200m.

The tunnel has taken 20 years of planning and construction.

But this is not the last word. An even longer link is well underway from Austria’s Tyrol to Italy, and significant works continue on the French Frejus project between Lyon and Turin, 57km long like the Gotthard.

Gotthard’s AlpTransit client, meanwhile, is completing work on a shorter but significant 16km long complement at Ceneri further south, and two other long and deep rail tunnels are in construction in Austria.

Another has just begun in Norway, which is also building the world’s deepest undersea road tunnel. Sweden has begun its giant city bypass project for Stockholm. Germany’s complex multi-tunnel Stuttgart 21 project is in full swing, and Italy is beginning work with the biggest TBM (tunnel boring machine) seen in Europe.

The €8.5 billion Brenner base tunnel will be a record too when complete in 2025.

Its basic length is 55km between main portals at Fortezza in Italy and Innsbruck in Austria, but a connection into the 9km Innsbruck bypass tunnel means a total 64km of underground travel for some high-speed trains.

The depth will be 1,800m beneath giant mountains, and the challenges for excavation and operation include hot rock conditions near to those on the Swiss project, and possible bursting or squeezing ground.

Access tunnels are complete or in construction, including a new service and safety tunnel alongside the existing twin track Innsbruck bypass, as well as smaller tunnels for waste disposal.

Exploration

Five main project sites are busy, at the two portals and three intermediate lateral access tunnels, to twin single bore main drives. These are 8.1m inner diameter, and between 40m and 70m apart. A smaller 5m diameter tunnel runs between and below the main drives, for exploration initially, and then drainage and access in the operational period.

Big challenges have included crossing a severely crushed zone of rock in the Italian half of the project – a 1.5km sector that could have stalled the whole scheme now successfully excavated with drill and blast (D&B), both for the exploratory tunnel and the main drives.

Current €380 million works at Innsbruck will also drive a 15km long extension to the initial 6km exploratory tunnel southwards, using a Herrenknecht hard rock TBM. Its unshielded front section allows detailed inspection of rock conditions to inform main drives later.

But this summer, the big contracts for the main drives were being let, said Brenner Base Tunnel spokesman Simon Lochmann.

“On the Austrian side, the Wolf access is essentially finished and we are ready to tender the Austrian main section from there, with 9km of the exploratory north and south, and then the main bores too. It is an estimated €1.3 billion,” he said.

On the Italian side, one of the biggest contracts has just been let to a five-firm consortium including Astaldi, Ghella, Oberosler Cav Pietro, Cogeis and PAC, a €1 billion package for 15km of exploratory tunnel and 40.3km of main tunnel, as well as an emergency station cavern.

Work has also begun on complex portal works at the south end, including ground freezing to take the tunnel underneath a river.

For the €8.8 billion French-Italian Frejus project between Turin and Lyon, most of the exploratory and access tunnels are finished, and a first main bore is underway on the French side. The inner diameter will be slightly larger than Gotthard and Brenner, giving clearance for lorry shuttle trains.

This first 9km long section is intended first as an experimental bore through possibly squeezing ground, testing TBM performance, but will later be part of the route.

Specially designed

Contractor Spie Batignolles is using a specially designed high-powered TBM from French maker NFM with capacity to “overcut” up to 11.26m diameter to allow for ground convergence. Christened Federika, it arrived in the summer and has begun its drive.

The AlpTransit project, meanwhile, continues with the 15.4km long twin bore at Ceneri which will take a further ten minutes from the Zurich to Milan route. Drill and blast with Sandvik rigs and a Rowa backing train finished in January when the two difficult 8km northern drives broke through. Two southern drives finished last year.

“Lining is almost complete,” said AlpTransit project manager Paolo Vicentini, with the tunnels readied for track and electrical work. Satisfaction has been marred somewhat by a tragic fatality, he said, when a tunnel miner was hit by a reversing spoil truck.

In Austria, meanwhile, two more major deep tunnels are underway. One is the 32.9km Koralm for a completely new high-speed rail link between Klagenfeldt and Graz.

The twin bore tunnel runs up to 1,250m below the 2,000m high Koralpe mountains, causing some rock convergence. Though the “hot rock” problem of the bigger tunnels is present, it is less extreme.

Contractor Strabag has struggled with two 17km-plus long drives on the overall 19km central section through difficult hard, tough and blocky rock, using two 9.9m diameter CREG-Wirth TBMs (formerly Aker-Wirth).

Progress has been steady since they set out in mid-2012, but slower than expected. The 9.7m diameter machines install a segment lining.

The TBMs have currently reached a point 19km from the tunnel portal, said the project director for the overall Koralm project, Klaus Schneider, from client Austrian Rail’s infrastructure division ÖBB-Infrastruktur. That leaves just under 2km to go on each drive.

Drill and blast work is also underway on a 900m long safety station between the two parallel TBM drives.

On Koralm’s west side, Austria’s Porr has been working since 2014 on a 12km drive for the south bore with a multimode Herrenknecht TBM. The other bore was part excavated to over 6km early on for exploration, and is being completed by drill and blast.

Porr has done 3km with the TBM, which shortly has to be converted from soft ground EPB operation to the hard rock further in. The D&B bore is at the 9km point so far.

Despite slow progress, both the tunnel and the overall railway scheme remain within the overall completion envelope, said Schneider.

Not content with two deep tunnels, Austria embarked on the 27km long Semmering project in 2014, 800m deep and straight underneath the historic 1854 Semmering mountain railway between Graz and Vienna – a scenic but difficult sinuous line. Geology here is heterogeneous with multiple faulting and water saturated rocks.

Conventional drive

Three major contracts are using conventional methods to get through, though a TBM can be used for a central 9km section, the Fröschnitzgraben. For this, access has to be gained via two completed 400m deep shafts, begun in 2014 by a joint venture of Implenia and Svedelski, which is now working on the TBM launch cavern. The joint venture will also do 4.4km of conventional drive for the twin tunnels in the other direction.

A 7km length from the Gloggnitz portal is underway by a joint venture of Implenia, Hochtief Infrastructure and Thyssen Schachtbau, using mainly drill and blast and currently about 900m in.

A final section, also a 7km conventional drive, is by Swiss joint venture Marti with Marti Tunnelbau, and began in May this year.

Norway has also embarked on a high speed line, the 22km long Follo line project, with twin bores running 20km south from Oslo to Ski, through a low mountain. It is not a deep line, at less than 100m depth.

Four Herrenknecht 9.9m diameter TBMs were assembled this summer in two linked 54m long caverns at a central access halfway along the main 18.5km tunnel section.

The Spanish-Italian joint venture of Acciona Infraestructuras and Ghella worked with lift contractor Mammoet to put together the huge components. The two pairs of TBMs were setting out north and south this autumn for approximately three years of excavation.

An additional 1.5km section continues the tunnel near to Oslo. Italian contractor Condotte D’Acqua is using drill and blast thread through a complicated spaghetti of existing tunnels. It is also using rock splitting to avoid vibration close to existing road and water routes, using hydraulic Superwedges from Italian maker Ripamonti.

Norway usually favours drill and blast, but two more TBMs have also been working lately. First is another Herrenknecht on a railway project into west coast city Bergen, where a second bore will relieve congestion on the existing single track Ulriken tunnel. Sweden’s Skanska and Austria’s Strabag are about halfway along the 7.5km drive at present.

The client side project manager for the scheme, Hans-Egil Larsen from Norway’s National Railway Administration, said a TBM was better because the new bore was only 30m from the old line which must continue running. Drill and blast vibration would have been disruptive.

Hydroelectric

Further north, a 7.2m diameter Robbins main beam machine broke through last December for the 7.4km long headrace tunnel on the Røssåga hydroelectric project.

Its nearly two-year drive had involved “boring through quartz-rich rock up to 300MPa, as well as softer karstic limestone with water ingress,” according to Tobias Andersson, TBM manager for contractor Leonhard Nilsen & Sønner.

Norway’s traditional drill and blast is being applied further south in oil port Stavanger. The NOK6 billion (€700 million) Ryfast scheme is a three twin-tube tunnel project to connect western suburbs across a surrounding deep fjord.

Two tunnels are 4km and 5.5km, but the main Solbakk tunnel will be 14.3km long, diving 290m deep. Cross section is small, however, at 8.5m width after lining, with two 3.25m traffic lanes in each bore.

Work is in two halves with Swiss firm Marti beginning the eastern side in August 2013 using a Marti Technik conveyor system and Sandvik drill rigs, and FA Gruppen using an Atlas Copco drill at the other with more traditional truck mucking out.

Two main types of rock are present, hard gneiss on the eastern side, and a softer phyllite claystone on the west.

Project director for the overall scheme Gunnar Eiterjord, from client Statens Vegvesen (the Norwegian Public Roads Administration), said that currently around 12km of the 14km had been excavated and that progress was good.

Bigger and deeper

An even bigger and deeper project is in final design preparation, however, as part of Norway’s no-ferries E39 west coast highway scheme. The Rogfast, running north out of Stavanger, will be 25km long and 380m deep below the sea.

Next door, Sweden is busy too with initial works begun on the massive Stockholm bypass this spring, blasting access and works tunnels and caverns.

The ten-year project is for a full dual three-lane highway running nearly 20km in twin tunnels around the western side of the city to alleviate severe congestion. The city is set within an area of Baltic islands and inland lakes which, while scenic, leaves it with only three connections north to south.

To bypass the capital, the new motorway must go up to 70m underground below royal parkland and nature reserves on islands to the west.

Major junctions will also be partly underground, using an additional 14km of ramp tunnel, and there is further work for seven access tunnels. The client, the Swedish Road Authority, is letting six major tunnel contracts at present, each around €300 million, and six for junctions to start shortly.

Early work for access is under several smaller €50 million range contracts, including with Czech contractor Subterra at the southern end.

Germany, meanwhile, is pressing on with the multiple tunnels of its €5.8 billion Stuttgart 21 underground station project and the associated Stuttgart-Ulm high-speed rail scheme with four major tunnels.

The first of four TBM sections are complete for the 9.5km long Filder tunnel, Stuttgart 21’s most difficult.

The 4km drive towards the city from the airport finished earlier this year just before entering a region of expansive anhydrite rock. The calcium sulphate expands strongly if it is saturated with water, and NATM (new Austrian tunnelling method) with modified drill and blast and special measures are being used to prevent water ingress.

The TBM, meanwhile, has been pulled back by contractor Porr, leading a consortium on the work, and is just under halfway along the second bore’s first drive.

The central NATM section must be complete by the time it gets there because the TBM will be pulled through the 2.5km length to continue the bore on the far side of the sensitive rock area with a further 3.6km drive. Then it turns around to go back uphill for the last section of the first bore.

Around Stuttgart station, major soft ground NATM caverns have been completed for work on the lines into the station. From these extensive compensation grouting will be done.

Dry work is also needed on another of the surrounding tunnels, the Feuerbach which also has anhydrite, according to drill maker Sandvik. Working with drilling subcontractor Avesco, it has specially modified drills, refitted with air cooling for the hydraulics and air flushing for the boreholes with additional dust filters.

Avesco has also done substantial work for main contractors Züblin and Max Bögl on one of the major tunnels for the €3.3 billion high-speed line connection to Ulm from Stuttgart suburb Wendlingen. Some nine Sandvik machines have worked on the 5.3km long Albabstieg tunnel into Ulm from the Schwäbishche Alps highlands.

Austria’s Porr, leading the same team as at Filder, is well advanced on the two tunnels which climb the highland – the 8.8km long Bossler, and the 4.8km Steinbühl.

The Steinbühl, excavated by drill and blast, has almost completed lining work for the bores. Bossler is finished for the first of two bores where some 7km has been done by a Herrenkencht EPB (earth pressure balance) machine, 3km more than originally supposed. Squeezing ground conditions have not been as difficult as expected and drill and blast was not needed.

Work has just begun by contractor Implenia on the last of the major tunnels, the 8.2km Albvorland tunnel through softer ground closer to Wendlingen before the Schwäbische Alp section, according to a spokesman for client Deutsche Bahn.

Two TBMs will drive simultaneously to ensure relatively fast completion as this tunnel is on the critical path.

Finally, Herrenknecht is readying Europe’s biggest TBM ever for the 7.52km long Santa Lucia road tunnel near to Florence in Italy.

The contractor is Pavimental. At a diameter of 15.87m, the EPB machine is 200mm bigger than Herrenknecht’s previous largest, used in the Italian Apennines, on the now complete Sparvo tunnel.