Tunnelling: Digging deep

At least half a dozen tunnel projects of world significance were underway or starting in Europe this year, including world record length road tunnels in Norway, the giant peripheral metro scheme in Paris, France, two transalpine high-speed rail projects, the world’s biggest TBM (tunnel boring machine) driving a road in Italy, and one of the world’s biggest sewers – the 25km Thames Tideway in London, UK.

Scandinavia remains a major centre for work at present, and one of the most dramatic projects now getting fully into its construction stride is the 20km-long Stockholm bypass in Sweden.

This giant scheme for an underground motorway is carving twin three-lane wide tunnels up to 70m down through mostly hard rock to the west of the capital, passing under parkland and royal palaces.

Work includes three major interchanges, all or partly underground too, involving 19km of ramp and access tunnels.

Long in design, the project started construction in 2016 on several access tunnels, with main tunnel excavation starting last year.

The 12 major contracts are let, with six underground sections in full swing with drill and blast excavation near peak production, according to tunnel manager Erik Lindgren.

“We have at least 20 drilling rigs operating, including 17 big three-boom machines,” he said. Not surprisingly most of these are from Atlas Copco having been made in the country.

“Of a total 59km of tunnel, we have done around 30% at present,” he said.

Three jetties for spoil removal by barge from the islands the project passes through are now operating.

Faultline

A particularly challenging section of the work is under a lake channel in the south end. A faultline is bigger than expected, with around 30m filled with soft erosion debris.

Excavation requires significant spiled roof support and a redesign to add a permanent waterproof concrete lining. Most of the project in hard granite requires only shotcrete.

To prevent too much delay, small parallel side tunnels have been added to the scheme said Lindgren. These 35m² cross section bores, now almost finished, will initially allow advance exploration, but will mainly be used to take the jumbos 180m around the stalled section to continue the main drive in good rock ahead.

Norway’s schemes are also impressive. Near Oslo is the 20km long twin bore Follo line high-speed rail project where four hard-rock TBMs have been driving an 18.5km-long section north and south from a central access point since autumn 2016. The first two 9.9m machines heading north towards the capital through mostly tough gneiss, broke through in early September. The double-shield machines are currently being dismantled for a buy-back by manufacturer Herrenknecht.

The others are “doing nicely” on the southern drive, according to BaneNor, the country’s recently renamed railway authority, which is the client.

“They are expected to breakthrough early next year,” it said.

A final complex 1.5km section of the tunnel is by drill and blast. Though 70% complete it has been slowed up by financial problems at the contractor Condotte, with remaining work re-tendered.

Norway has also begun a major road tunnel which at 26.7km long and running up to 392m below sea level, will be a world record length and depth for a subsea road tunnel. The tunnel will carry the country’s main E39 West Coast Highway across the mouth of the big Bokna Fjord just north of oil industry city Stavanger.

It is the first of seven major fjord crossings for the multi-billion Euro No Ferries project to make the highway continuous, past Bergen and all the way to Trondheim.

The tunnel will have a midway point at the island group of Kvitsøy, where a major underground interchange connects to the island community by a 4km spiral tunnel.

There will be two 10m-diameter shafts from the surface here for ventilation. Traditional drill and blast is being used for the twin 10.5m-wide tunnels. Initial access side tunnels are just completing, and the first of three main drives just let.

Sweden, meanwhile, is finishing another albeit shorter twin three-lane tunnel for the Göta älv river at the west coast city of Gothenburg. This is an immersed tube crossing with three 100m segments cast in a nearby drydock before floatout and immersion. German contractor Züblin used Peri formwork for the operation. The tunnel opens in 2020.

Main station

In Germany, attention is focused on the huge Stuttgart 21 project and its associated high-speed rail link to Ulm. The controversial scheme, underway for some five years, is putting the city’s main station underground with a score of lines ending at the old terminus being made into through lines, allowing a reduction of platforms to eight. Local, regional and high-speed lines are all going underground in a series of tunnels in the city’s soft ground.

The biggest, however, is the complex 9.5km twin bore Filder tunnel through surrounding hills to connect high-speed lines to the airport and then onwards to Ulm.

Another half a dozen tunnels of up to 8.8km long are needed for the Ulm line, putting a total 27km of its 58km underground.

Filder has been driven in six sections – the two in the middle by drill and blast because of reactive anhydrite rock, and the rest by a Herrenknecht dual mode TBM. This completed a first 3.5km section of the eastern bore in EPB (earth pressure balance) mode and, after withdrawal, did the same on the western bore, where it was then pulled through the dry section to finish a second downhill drive part in open mode. Breakthrough was in July.

Tunnel contractor Porr is currently turning the TBM to drive uphill again for the last 3km section of the eastern bore. The NATM (new Austrian tunnelling method) built cavern for the turn operation will become part of multi-line underground approaches to the new station, which has been excavated over the last two years by cut and cover.

The scheme is currently costed at over €8 billion – almost twice the original estimates – and its opening will be delayed until 2025.

The link to Ulm has seen less cost increase and remains near the original €2 billion. Significant achievements this year include the completion in June of the second bore on the 8.8km-long Bossler tunnel by the Porr led ATA Tunnel Albaufstieg joint venture, using an 11.3m-diameter Herrenknecht EPB TBM.

The machine also bored 7.8km of the first, after managing to pass squeezing ground it was originally thought would require traditional methods.

Parallel drives

Two other Herrenknecht machines are currently at work on parallel drives for the shallow 8.2km Albvorland soft ground tunnel closer to Stuttgart, running alongside the A8 autobahn. The EPB machines have driven “about half the length” for each bore, said client Deutsche Bahn.

Further south, Austria is also continuing with major rail line projects, including the Koralm, Semmering and, not least, the gigantic Brenner pass Alpine link, which at 64km – including a bypass for the town of Innsbruck – will be the world’s longest transport tunnel.

Koralm, a 32.9km twin bore base tunnel for a completely new 130km-long high-speed line between Graz and Klagenfurt has been a challenging drive, particularly for contractor Strabag on the longest central section, which is up to 1,200m deep. Blocky, squeezing and sometimes very hard rock proved hard work for its two 10m diameter Wirth TBMs.

Both started in 2013 and the first completed its 17.1km drive early this year. The drive was slightly longer than initially planned, with an extension to speed up completion of the northern bore, which is still being driven from the western end by a third machine.

The second TBM broke through this autumn, connecting to a completed section of the southern bore, Austrian rail client ÖBB Infrastruktur reported.

Convertible machine

Meanwhile, work on the final western section of the north bore in the third contract is being achieved with a Herrenknecht convertible machine by contractor Porr.

After 4.5km in softer ground, it broke into a shaft for conversion to hard rock mode. It has since made about 2.5km, with 5km to go. It faces similar tough ground challenges.

The Semmering tunnel north of Graz on the Vienna line is at least as challenging, although it is shorter at 27.3km and not quite so deep. But geology is tricky, sections face high water pressure and access is difficult.

Two 7km contracts are underway at the tunnel ends, each by drill and blast. The eastern Gloggnitz started in 2015 at the portal, and also from a 1.1km intermediate access tunnel with two 250m-deep shafts.

The Implenia, Hochtief Infrastructure and Thyssen Schachtbau joint venture has excavated about 3km so far from the portal, and is just completing the shafts.

The other end, Grautschenhof, was begun in 2016 by Swiss joint venture Marti, with Marti Tunnelbau. It has built two 100m-deep shafts at halfway along from which conventional excavation is underway in both directions, with about 500m completed in each direction.

Fröschnitzgraben, the biggest contract in the middle, is being developed from a high valley via two 400m deep shafts.

A complex of caverns up to 16m high and 20m wide has been excavated beneath, the biggest later to be the central emergency rescue chamber. In this complex, two NFM single-shield TBMs have been assembled. The first set out in midsummer, and has made 500m progress, while the other will start shortly, also heading east.

In the other direction, conventional excavation is underway and has made about 1km so far in potentially difficult ground.

Meanwhile, Austria’s biggest project, in tandem with Italy, is the transalpine Brenner base tunnel, which is now in full construction along the whole 55km main length, and with the connecting 9km Innsbruck bypass tunnel upgrade almost complete.

By October, 85km out of 230km of tunnel had been excavated – over 50% of the small central exploratory and just under 20% of the main 9.5m-diameter tunnel tubes.

Main works for the Austrian side have just been awarded to a joint venture – Porr-Hinteregger-Condotte-Itinera – bringing the total let to 85%.

The huge €966 million six-year long package includes 37km of the twin main running tubes between Pfons and the Brenner pass, plus 9km of lower exploratory tunnel between them and an emergency station St Jodok.

On the Italian side, the biggest contract of all, the €993 million Mules 2-3 has been underway for two years by an Astaldi-Ghella led joint venture. The seven-year construction is for 39.8km of main tubes and 14.8km of exploratory tunnel, plus an emergency stop cavern in Trens. It extends from the southern river underpass contract to the border.

Complex work featuring jet grouting and ground freezing is needed for the alluvial ground of the final section underneath the Isarco river. Four 25m-deep shafts are reaching completion, and they allow tunnelling through rock beneath. The project includes a short section of the main tunnel bores.

Italy, too, has other major works, the biggest the €6.2 billion Terzo Valico rail tunnel on the new Milan-Genoa high-speed route. The 27km, 250m-deep tunnel through high hills around the port extends further after a few hundred metres into the 7km Serravalle, making a total link of 34km.

Serravalle is just beginning construction with two 9.7m Herrenknecht EPB TBMs heading south.

The main contractor, Salini Impregilo Consorzio Collegamenti Integrati Veloci (COCIV), is in overall control of the project and is doing most of the main tunnel by conventional excavation. This is primarily because of difficult ground conditions in mixed metamorphic rocks. The contractor is working from two access tunnels, and just beginning from two others and the south portal.

More suitable sandy marls allows the northern 7.7km section to be excavated by TBM under a subcontract with Seli Overseas, which also does the Serravalle. The first of two further EPBs began in late 2016 and has achieved 3.5km, while the other started a year later and is 900m in.

Biggest TBM

Italy is also the location for a drive by Europe’s biggest TBM. At 15.87m in diameter, the Herrenkencht EPB began a 7.52km-long drive 18 months ago for the Santa Lucia motorway road tunnel south of Bologna.

The width allows for a three-lane northbound section for the upgraded A1 motorway link through the Apennines towards Florence. The existing two-way tunnel will be renovated for traffic the other way.

Difficulties include possible methane, for which the machine has a special trap mechanism, and tunnel ground cover of just 11m in places – though the maximum is nearly 300m. The drive began in soft clay, but 75% of the drive is limestone.

Italy is also a partner for Europe’s third major transalpine rail tunnel for a high-speed link from Turin to Lyon in France. Various access and test tunnels have been completed, and a first 9km-long single bore of the twin main tunnels has been underway at the French end since 2016 as a test project for difficult squeezing ground.

The drive is using a specially designed NFM TBM with an overcut capacity of up to 11.2m for the 10.5m diameter drive. The contractor is Spie Batignolles.

The client, Tunnel Euralpin Lyon Turin (TELT), said, “We had a difficult section of ground in waterlogged carboniferous rock at the end of 2017, and there was substantial overbreak pulling out far too much spoil. It held things up for three months, but the machine is currently making 10 to 15m a day, and we are at approximately the 5km point.”

A newer concern over the continuation of the project at present is because of objections by part of Italy’s new Liga-Five Star movement government, which may seek to cancel the work. But that is still in the air.

Work in France is more certain on the Grand Paris Express. This is a set of four new metro lines complementing the capital’s existing radial metro with a ring of lines around the city and connections to isolated suburbs not served at present. Of the 200km of new line, most is underground, along with 68 stations.

Some of the work must be completed for the French Olympics in 2024, but the project will continue to 2030.

Significant construction is already underway, with eight contracts let on the Line 15 South. The first drive began in April, and a second machine set out recently with a total of five to be working next year. Herrenkencht has the majority of the orders for these EPBs. Tunnels are 9.83m in excavation diameter, accommodating twin tracks.

Four stations

For Line 16, which heads north, a first contract was let earlier this year with a second major section in late October to Italian contractor Salini-Impregilo for €719 million. It includes civil work on four stations and 11km of twin tunnel to be built with two TBMs. Additionally, vertical shafts are being made with a Herrenknecht VSM (vertical shaft machine).

Work is also underway on a link to Orly airport, extending the existing Line 14.

Another capital, London, UK, is embarking on its next big tunnel works following the delayed but completed Crossrail scheme. This new project is Tideway, a 25km long sewer interceptor along the river Thames, mostly at a diameter of 7.2m, picking up a series of major sewers that currently discharge into the river during flood conditions.

The client is utility Thames Water which has a number of major sites along the river for shafts and other works, but the key location at present is at Kirtling Street, near the well-known former Battersea Power Station.

Here the main TBM drives for the central tunnel section will start out from already completed shafts.

The contractor is a Ferrovial Agroman UK and Laing O’Rourke joint venture, and it lowered the NFM made TBM components to tunnel level in September 2018 for the assembly of the 8.8m-diameter machines, which start drives later this year.

Four other TBMs will make drives for the project – one 8.8m, one 8.1m, a 6.4m, all Herrenknecht, and a smaller 2.6m refurbished Lovat.

Finally, the Czech Republic has recently

seen completion of a significant tunnel drive using a multi-mode TBM for the first time in Eastern Europe. The twin 4km bores are for a high-speed rail link between Rokycany and Pilsen, the republic’s fourth biggest city, in the west of the country, part of upgrading the country’s network.

The 9.9m diameter Herrenknecht worked first in EPB mode through mixed ground and then open shield drive mode. Contractor Metrostav used the EPB for the quartzite shale stone and clay soils for 3km, and then converted the operating mode to open shield the last 1.1km of each of the twin bores where they went through hard spilite rock.

Following breakthrough at the end of last year, the tunnels are being fitted out.