Tunnelling: Digging deep

Tunnelling attention in Europe this year has swung from the Alps, following completion of excavation on the world- beating 57km long Gotthard high speed rail tunnel, to the UK with a focus on London, where construction of the huge €16.6 billion Crossrail project is just getting underway.
The 118km long east/west rail link has a highly complex 21km long twin bore central section passing right beneath one of the world's busiest and largest cities.
Some €183 million worth of design contracts have been under way over the last two years, with big consultants such Arup, Mott MacDonald, and Prescott Wilson, working to thread this line under, in and around multiple metro lines, power tunnels, station interchanges and other services.
Mainland European contractors are strongly represented. Spain's Dragados is being teamed up with Irish contractor John Sisk for the work on the tunnels running east. A joint venture of Netherland's firm Bam Nuttall, Spain's Ferrovial and the UK's Kier (BFK) has been chosen for the western running tunnels and station shafts, plus the sprayed concrete lining works for Bond Street and Tottenham Court Road stations - both in the heart of London's West End.
Austria's Alpine BeMo Tunnelling, the UK's Balfour Beatty Civil Engineering and Morgan Sindall, and Vinci Construction Grands Projects from France, have the remaining central tunnel section works, making access shafts and sprayed concrete lining works at Whitechapel and Liverpool Street stations. Finally, the €218 million River Thames crossing tunnel is in the hands of Germany's Hochtief Construction and the UK's J Murphy & Sons.

Big winner
One of the biggest winners, however, is German TBM (tunnel boring machine) maker Herrenknecht, which was awarded contracts in May for the EPB (earth pressure balance) machines by all the main contractors, so that all six TBMs will be built by the firm. The 6m diameter machines must deal with firm London clay, gravels and sands.
In September, it was announced that Herrenknecht's Schwanau factory would also be making two more TBMs, this time more complex slurry machines for boring the 2.6km long Thames Tunnel which passes through saturated chalk.
But while tunnel workers may be migrating to the UK, there is still plenty happening in the Alps.
Rail installation is now under way for the twin bores of the Gotthard and, just south of there, a further tunnelled link for this Swiss Alptransit high speed route is well advanced. The 15.4km long Ceneri is also a twin bore, passing under a 1,100m high mountain near Locarno, Switzerland.
Drill and blast drives are using primarily Sandvik 1300 three-boom rigs, with a long ceiling suspended back-up train system from Switzerland's Rowa Logistics. Two drives each, north and south, are heading out from a central cavern accessed by a side adit driven two years ago from the little village of Sigorino by a Robbins main beam machine.
Breakthrough is due in 2016. Some 37% of the total tunnelling has been achieved, slightly behind schedule but likely to be caught up to meet the completion date.

Alpine link
Another dramatic Alpine link has also been confirmed. The Austrian and Italian governments are now fully committed to construction of the Brenner Pass tunnel.
Like the Gotthard, this is a very deep-level flat-gradient tunnel up to 1,800m deep under the mountains. It will take heavy, fast freight trains and superfast 250kph passenger trains.
The 55km long twin bore tunnel is almost equal to the Gotthard in length. An existing bypass tunnel for the Austrian city of Innsbruck at the north end is to be linked in, and trains taking this route heading for Berlin from Italy will remain underground for 62.7km, which will mean a world record can be claimed in 2025.
Unlike the Gotthard, the Brenner will have a third central service tunnel that will be 6m in diameter.
Construction work has begun at each end of this, since it serves initially as an exploratory probe for rock conditions. A 10.5km drive from the Italian end was completed last year under an €80 million contract with a seven firm Austro-German-Italian consortium led by Pizzarotti and Condotte. Italy's Seli supplied the 130m long support train behind a reconditioned Aker Wirth cutterhead with a 6.3m diameter.
A 5.9km drill and blast southwards from Innsbruck has reached 3.5km so far, with none of the expected faults encountered in the quartz rock. This gives rise to hopes that main drives will later be able to use TBM rather than slower methods. The drives will shortly meet a 2.4km side adit from Ahrental being built by the same contractor. Other side links are underway.
The Brenner is part of a key route for the Trans European Transport Network (TEN-T) from Palermo in Sicily, Italy, to Berlin, Germany, and eventually Scandinavia.
For this, a number of tunnels have been underway in the Inn river valley north of Innsbruck to install a high speed underground line approach to the main base tunnel.
One of the last of several tunnels, the 8.48km Vomp-Terfens tunnel was completed in February, 2011, by Austrian contractor Strabag, with Züblin and Hochtief. The two- and three-track drive was through loose rock and some solid rock by NATM (new Austrian tunnelling method).
For the same route, German Federal Railways is currently building more than 20 tunnels on a new 85km section of high speed line between Nuremberg and Erfurt, and more on the link to Leipzig.
Though mainly small, they include the four significant projects on the southern section. They are the 3.8km long Eiberge tunnel and the 2.7km Reitersberg, both twin bore drill and blast projects, as are two longer ones - the 8.3km Blessberg and the 7.4km Silberberg.
Wayss & Freytag, Bilfinger Berger, Max Bögl and Bickhardt Bau are well advanced with the excavation, nearly complete in the Silberberg, and finished in Blessberg, which has had 60% of its inner lining installed.
There are three more tunnels on from Erfurt, two of which - the Finne at 7km and the Bibra at 6km - are almost continuous, with only a small valley separating them.
On the Finne tunnel, contractor Wayss & Freitag, in a joint venture with Max Bögl and Porr Tunnelbau, finished Herrenknecht TBM Mixshield drives last year and is now making cross connections by drill and blast. Lining work will be done in time for opening in 2016.

High speed rail tunnel
Meanwhile, another major high speed railway tunnel has started in Austria - the 32.5km long Koralm tunnel, which is part of the ÖBB Austrian railway's 130km route between Graz and Klagenfurt, which is itself a section of the Baltic-Adriatic Axis.
Germany's Aker Wirth won a contract in May with Strabag for two 9.93m diameter telescopic shield machines for the rock tunnels. They will start work in October next year on the main part of the tunnel work which is in Lot 2, the biggest contract on the scheme at €571 million. Switzerland's Rowa Tunnelling Logistics is supplying the backup train.
Freight lines are also of significance in Europe. France's Vinci Grand Projets, with Wayss & Freytag, and Belgian firms MGB/CFE and CEI-de-Meyer, has just completed drives on a new railway tunnel underneath the docks at Antwerp in Belgium.
Twin 6km long rail freight tunnels will service a huge container port. They must pass just under the river Scheldt and a wide ship canal with almost no cover. A huge concrete slab has been poured into a dredged space in the canal bottom to serve as a "roof" to stabilise the drives.
The two 7.5m Mixshield TBMs from Herrenknecht had to cope with high water pressures in soft sands and clays of up to 4 atmospheres. Drives were completed in May and July with an average 15m/day, and the machines were dismantled in August.
Four of 13 cross passages have been made and four more are in mid-construction. All the cross tunnels and an additional eight connections to escape shafts are being constructed by freezing the ground between the now completed main tunnel drives. The freezing process has begun for the next five cross links, using cold saline pumped through a pipe network to solidify and stabilise the ground before excavation.
In Italy, meanwhile, a 4,300 tonne world record giant of a machine, a 15.6m diameter EPB from Herrenknecht, is pressing ahead with the first of two 2.5km drives for the Sparvo tunnel on Italy's A1 Autostrada upgrade in the mountainous area between Bologna and Florence.
Each tunnel will have two lanes of road and an associated emergency lane, requiring a finished width of 13.6m. Contractors Vianini Lavori, Toto Costruzioni Generali, and Profacta started the drive in August.
In Rome, three of six Herrenknecht EPB machines are continuing drives on metro extensions. Three others completed work last year.
Also in Italy, work is underway on the A3 Autostrada from Salerno to Reggio Calabria and Cosenza - an 11km long, €226 million road scheme.
It has a total of 5.9km of large 14.9m tunnels being driven by drill and blast through broken puckstone (calcareniti), dolomite and flysch. A joint venture of Uniter and Cometal is carrying out the work using two Sandvik DT1130 jumbo rigs.

Breakthrough
In Spain, work on the expanding high speed rail network, one of the biggest in Europe, is continuing.
In Barcelona, July saw the breakthrough of an underground connection through the centre of the city to carry twin lines from the central station north-eastwards. This will eventually connect 130km to the French border from the Madrid to Barcelona line.
The 5.6km long Sants to Sagrera tunnel was one of the most monitored and controlled tunnel drives in the world because it passes right by the famous Sagrada Familia church and another famous building designed by the architect Gaudi.
A deep pile wall was built alongside the church to protect it. Contractor Sacyr used a Herrenknecht EPB to avoid settlement on the 5.1km drive through gravels and clay. Almost no measurable settlement was detected, to the satisfaction of the Spanish high speed railway authority Adif and many others.
Excavation for another under-city high speed link, this time in Madrid, was completed in February - yet again using a Herrenknecht machine. The 7.3km Atocha to Chamartín connection links six different high speed lines to the capital, allowing through train passage.

Major projects
Significant work is underway at the other end of the Mediterranean in Turkey. Major projects include the three-year long Akeli-Hitit Aslancık hydro-electric plant project where three Sandvik DD320-40 jumbos and a DX700 have been in operation since September last year. They are working on a 13.7km main tunnel of 6.5m diameter, plus a 1,700 m approach tunnel. Project cost is €138 million.
The Ak-eli & Hitit contractor joint venture faces sudden water discharge and clay bands in the mainly marble, granite and basalt rock. The client is Anadolu Holding, Doğuş Holding and Doğan Holding.
Three Robbins machines are also being readied for hydro-electric work in Turkey. A 10m diameter double shield TBM is to drive an 11.6km headrace tunnel through volcanic based rock with limestone and marble for a hydroelectric scheme in Corum Province. The machine is being assembled on location using Onsite First Time Assembly (OFTA).
At Dogancay hydroelectric project, a 4.2m Robbins double shield is being assembled in the same way for a 7km headrace tunnel at the 62MW scheme. Another 4.2m double shield TBM will drive a 14.8km headrace at the 81.3MW Yamanli 2 station on the Goksu River.
Turkey also sees continuing work on the Marmaray Bosphorus rail crossing, where 1.8km sections on the European side between Yedikule and Yenikapi are being completed using a Caterpillar Tunnelling (formerly Lovat) 7.9m diameter TBM carving through hard silt, hard sandy clay, hard clay, lenses of limestone and some gravely sand. First of the twin drives is complete and the other is 60% finished. The contractor is Gama-Nurol JV.

Complexity
In the far north, Scandinavian contractor NCC's Swedish division says a major project on Stockholm's underground Citybanan rail scheme is the most complex it has done.
Up to 40m under the existing central station, it is carving out a new city station, and a variety of tunnels for pedestrians, track, stations and services, escalators and lifts -altogether approximately 510,000m3 of rock excavation. Station tunnels are up to 25m wide and 9m high, with double track tunnels 12m width and 7m high.
The typical hard rock of Sweden, good quality crystalline granite and gneiss, is being drill and blasted using Atlas Copco jumbo rigs.
The client is Trafikverket and the designer is WSP. The cost of the project €176 billion and the Citybanan is estimated to be finished by 2017.
Two interesting city rail projects are underway in Moscow. The first has involved the use of a large 10.9m Caterpillar EPB carrying out 100m long drives at a 30° angle to form entrances to metro stations. So far, two drives have been completed by contractor Mosmetrostroy.
A 6.6m diameter Robbins EPB with a mixed ground cutterhead will excavate urban rail tunnels for contractor Engeocom between new station sites in downtown Moscow. It will form two 2km long portions through clay, sand, pebbles, and limestone, beginning in May next year.
Robbins engineers will also be rebuilding a Cat EPB and designing a customised mixed ground cutterhead with 17in (432mm) disc cutters and carbide bits for the same metro line.
The machines will use continuous conveyors for muckout.