Tunnelling: infrastructure continues

Tunnelling is pressing ahead throughout Europe for metros, railway links and road crossings, by both tunnel boring machine (TBM) and conventional drilling – some on a significant scale, like London’s huge Crossrail scheme.

Others will eventually establish new world records, for length in the case of Austria’s Brenner Pass rail tunnel, or Italy’s Sparvo road project with the world’s biggest TBM.

The Brenner Base Tunnel between Austria and northern Italy is the largest scheme. Like the similar Gotthard tunnel in Switzerland, which completed excavation in early 2011 and is now being fitted with rail lines, the Brenner is exceptionally deep and long.

It includes a bypass for the city of Innsbruck and will total 64km, which is 7km more than Gotthard’s current world record of 57km.

To create the flat gradients which will allow high-speed passenger and freight, its twin 9.5m diameter main bores will run at depths up to 1,300m – slightly less than the Swiss tunnel but still posing problems of very high rock pressures and, perhaps, significant rock temperatures.

But all that is to come, with TBM drives probably starting in 2015 or 2016. For now work has been underway on assorted probe and access tunnels for the main drives.

The Brenner will have a 6m diameter central service and drainage tunnel between the main bores. It is being driven first to investigate rock conditions – already a 10.5km Seli TBM drive section has been made at the southern Italian end, with a 2km long side access. At the northern end, a drill and blast tunnel goes through potentially difficult ground starting at Innsbruck. Sandvik rigs are used.

Simon Lochmann, spokesman for client company BBT SE, said, “We just broke through in October with a major side access tunnel 2.4km long from Ahrental that joins the Innsbruck service tunnel.”

Four other access adit works are underway, he said, the most important being a continuation of the southern drive into a difficult zone of crushed rock “where the African and European tectonic plates interact”. This could stall a TBM drive completely.

So far this exploratory work, by drill and blast, has gone well through one 12m-thick sandy zone, with one more very difficult zone expected. The project is also building the first 2km of the main drives by drill and blast back to the southern portal, and two large caverns where the main TBMs will be assembled.

Gotthard fit out

In Switzerland, the Gotthard project continues fit out. This crucial European strategic high speed rail link from the north to Italy also comprises several smaller though significant tunnels. The largest is the 15.4km long Ceneri tunnel to the south, a twin 8.5m diameter bore that began in 2010 using four Sandvik 1300 three-boom rigs for a drill and blast operation working north and south from a central cavern. Rowi supplied roof-hung backup trains.

Drives by a joint venture of contractors Condotte D’Acqua and Cossi have been going reasonably well, according to client Alptransit’s project manager Paolo Vicentini. Difficult ground requiring heavy support has slowed the northern drives, though. These have reached 2.7km on the west drive and 3km on the east from a total of 8km. Southern drives are at 3km on both sides.

“We have also finished the short portal drives in the south, just over 300m long, and the 750m long drives on the northern end,” he said. These were separate contracts, and lining work is underway.

Another major Alpine project, also for a European Union transport corridor, is the Koralm railway tunnel for Austrian state rail company OBB, to link Graz and Klagenfurt. The 32.5km-long tunnel will be organised under three contracts – the first and largest a 20km-long section let for €570 million at the end of 2010 to contractor Strabag leading a consortium with Jäger.

Early work has concentrated on creating twin linked 20m diameter shafts 60m deep, the only access to the tunnel line, and a total 4.5km of tunnelling in soft ground for the two bores, using NATM (New Austrian Tunnelling Method) techniques.

Drill and blast work will follow to make starter chambers for two 9.9m diameter double shield hard rock TBMs from Aker-Wirth of Germany, which will make 17km and 15.5km long drives. Two Atlas Copco boomers, a Liebherr excavator and a BASF Meyco Robojet for shotcreting are doing the chambers for the launch of the first machine in January.

Meanwhile, also in the Alps, Condotte has been using a refurbished double shield hard rock TBM from Caterpillar Tunneling (formerly Lovat) to complete new emergency and reserve tunnel running 5.77km parallel to the Great St Bernard road tunnel between Italy and Switzerland. The safety tunnel is linked every 240m by 23 individual passages.

The 4.26m diameter machine drive, which began in October 2010 and finished this June, was through gneiss, schist and sandstone, with hardness from 40 up to 140Mpa and with rock cover reaching 950m. The tunnel is lined by four-piece trapezoidal precast concrete segments.

Elsewhere, major rail tunnel projects are underway. In France, the first of two parallel 4km bores for a high speed tunnel under the Vosges Mountains was completed in August by a consortium of Spie Batignolles TPCI and Dodin Campenon Bernard, using a 10m dual mode Herrenknecht TBM which launched in November last year.

After 200m, the machine was switched from earth pressure balance (EPB) mode for mixed unconsolidated sandstone and limestone to hard rock driving for the remaining hard red sandstone. The tunnel will be part of a 106km high speed section completing the TGV route from Paris to Strasbourg.

Crossrail machine

Meanwhile, the fifth of eight Herrenknecht TBMs for Europe’s largest scheme, the £16 billion London Crossrail project, has recently completed testing at the Schwanau, Germany, factory. Christened Sofia, it is a closed mode slurry machine for a 2.6km long underground section passing underneath the River Thames in chalk.

Four other EPB type machines have already been delivered, the first two currently driving on the west side of London. The first of the 7.1m diameter machines began in May.

Keith Sibley, Crossrail area director west, said, “Our first TBM, Phyllis, has now successfully reached Paddington, having carefully navigated under London Underground’s Hammersmith & City line and the Great Western main line.”

A second TBM, Ada, has begun work but was halted 150m from Paddington in early October because of the collapse of a spoil handling hopper. Build up of spoil on site meant it could not proceed until the problem was resolved, though Crossrail said the overall programme was not affected. The tunnels between Royal Oak and Farringdon will be completed in late 2013.

Two machines for the eastern drives 8.5km towards Farringdon are currently being assembled underground, in two 30m diameter shafts joined by a NATM-excavated connection.

Another major city rail project is well advanced underneath the Swedish capital, Stockholm. The City Banan project has been planned to provide an additional twin underground rail connection through the city centre to provide relief for the existing main line.

The 6km project has some eight contracts, including a short immersed tube tunnel. But the two most critical are for hard rock excavation up to 40m deep in the city centre – one underneath the main central station, where an underground station is being built plus train tunnels, and one for a 2km-long tunnel section just north of that, underneath apartments and an existing metro station.

The new City station works are being handled by contractor NCC, with caverns and a variety of tunnels for pedestrians, track, services and escalators. Station tunnels are up to 25m wide and 9m high, with double track tunnels at 12m wide and 7m high.

The contractor has been using big Atlas Copco jumbo rigs for the drill and blast to make 510,000m³ of rock excavation in hard granite and gneiss. Around 90% was completed in October this year according to project manager Jan Uden, with bolting and concreting work to be done, followed by fitting out.

Good progress

Bilfinger Berger, meanwhile, has also been making good progress, with also about 90% of the excavation completed on the adjacent contract, where it has a total of 4.5km of double-track tunnel with a width of up to around 10m and a height of 6m to 8m, as well as a service tunnel alongside and assortment of connection tunnels.

It has been using Sandvik jumbos and, for some recent delicate work under a church and near the metro, has reduced vibration by using precise electronic controlled blasts using Edef detonators. The client is Trafikverket and the designer is WSP. The cost of the project is SEK1.8 billion (about £200 million).

Another northern hard rock city rail project has thrown up an interesting issue, this time close to Helsinki where a new rail link to the airport has been under construction since 2009. This includes an 8.4km section of twin-bore tunnel through granite in the airport area, driven by drill and blast in four separate contracts by Skanska Finland, SRT, YIT, and Kalliorakennus.

Most used Atlas Copco four-boom jumbos for excavation and bolting work, though Skanska worked with Sandvik machines, also four-boom. Work includes four underground stations.

Rock removal, just completed this summer, had to be extended in the airport zone because of an extraordinary problem of bacterial and mould growth in the tunnels. It was discovered that antifreeze glycol used on the planes had saturated the rock causing the growth.

Over a 1.1km section, therefore, the tunnel has been widened by an extra 1m from an original 7.5m width and 9m height, making room for an inner concrete tunnel to be built. This will be airtight to keep out smells and bacteria.

The tunnel fitting out work which has just started will also include nearly 2km of other special lining from the portals, which will insulate the tunnel from as low as -30°C.

Not everything is rail, however. The world’s largest TBM, a Herrenknecht EPB machine completed the first of two 2.6km drives in July this year for the Sparvo tunnel, one of a number of tunnels on a new 40km motorway section in the Apennines between Bologna and Florence. it will which upgrade Italy’s main spine A1 motorway through a better alignment.

Drill and blast

The huge machine was selected over drill and blast for a relatively short drive because its EPB mode helps avoid settlement, but also because of a methane risk in the ground. A special sealed spoil system vents and dilutes any gas encountered.

The monster machine presented unusual challenges to contractor Toto Costruzioni Generali, not least in turning its 2,700 tonne head section at the end of the drive to position it for the return parallel bore. Air cushion support units were designed by specialist firm Palmieri, well known for its cutter discs, which happens to be based in the area.

The machine head was successfully manoeuvred around on eight of these units. The operation nearly did not work after cracks appeared in the special flat concrete platform that was prepared at the portal but steel plates were slid in which could take the load, according to project engineer Lorenzo Scolavino. The contract value is €339 million.

In addition to these large projects, there are numerous other tunnelling projects currently underway or in their planning phases across Europe at the moment. For instance, Herrenknecht has just built a 12.56m diameter Mixshield for contractor OHL to build the first of two 1.2km bores for the Słowacki Route road tunnel under the Vistula in Gdansk, Poland.

Also in Poland, four Herrenkecht EPBs are currently driving the central 7km section of the Warwaw metro’s second line, a job that was covered in some detail in the July/August issue of CE.

US TBM maker Robbins, meanwhile, has recently supplied a 10m diameter twin mode double shield machine to Turkish contractor Gülermak for an 11.8km long headrace tunnel through volcanic rock for the Kargi Kizilirmak hydroelectric project in central Turkey.

According to the latest reports on the project, the machine is 350m in, making steady but slow progress through exceptionally difficult mixed weak ophiolite with high clay content and water inflows. Similar geology is expected to continue for the first 3km requiring segment lining.

Hard basalt will then be encountered for which the TBM will have rock bolting, ring beam and shotcrete equipment.

Another smaller Robbins is being readied in southern Turkey for the Yamanli hydroelectric project. The 4.3m diameter double shield TBM has to drive a 9.3km-long headrace tunnel through limestone for contractor NTF Construction.