Design considerations on approach to Brenner Baseline high-speed rail connection in Austria

Design considerations on approach to Brenner Baseline high-speed rail connection in Austria Feb 2008

Shani Wallis, Editor

A €2 billion, 40km section of new twin-track railway through the Lower Inn Valley towards the Austrian portals of the proposed Brenner Baseline tunnel connection to Italy, is built almost entirely underground. TunnelTalk travelled to Innsbruck to appreciate the undertaking and know how the project has influenced the criteria for design of future high-speed rail tunnels in Austria.

TEN axis Berlin to Palermo

Europe's continuing commitment to improving rail services places a continuous high capacity connection from Berlin to Palermo at the number one priority. Central to this ambition is the 56km long Brenner Baseline Tunnel through the Italian-Austrian Alps. That is the epic challenge yet equally demanding is construction of upgrades along the 2,400km corridor.

Long sections of the route in Italy and Germany are already complete with passenger and freight trains flying through substantial lengths of hard-won tunnels and subsurface structures. Today the effort is concentrated in Austria where attention is addressing capacity concerns through the Lower Inn Valley between the border with Germany and Innsbruck, Austria's gateway to the Brenner Baseline Tunnel.

Project data
€15 billion Munich to Verona high-speed rail upgrades in the overall Berlin-Palermo rail link in the EU's Trans-European Transportation Networks (TEN-T) strategy comprising the:

€3 billion Lower Inn Valley upgrade -
   €2 billion for Phase 1 - 40km of new twin track from Baumkirchen near Innsbruck to Kundl in the north-east; and
   €1 billion for Phase 2 - 22km of new twin track from Kundl to Kufstein at the border with Germany

€6 billion for the 56km long Brenner Baseline Tunnel, a 50/50 JV between Austria and Italy
   €4.5 billion for the Southern feeder line upgrades in Italy
   €1.5 billion for the Northern feeder line upgrades in Germany

Brenner Pass link - Munich to Verona

Lower Inn Valley Phase - Munich to Innsbruch

Being at the heart of Europe, the Inn Valley section is critical not only to the north-south Berlin-Palermo axis but also to east-west traffic. Currently the line carries 300 to 340 local and long-distance passenger and freight trains per day with some 12 million tonne of rail freight being carried on the existing 78km, hour-long trip up and over the Brenner Pass per year. This traffic load is set to increase steadily year on year and climb substantially once the 15-20 minute trip through the 56km long Brenner Base Tunnel opens and beings operation. Ahead of that, the first upgrade section of the Lower Inn Valley route between Baumkirchen near Innsbruck and Kundl just south-west of the main rail junction at Wörgl, will support an increased 400 train trips per day when it opens in 2012.

Valley feat
Building new rail infrastructure through Europe is not easy. As well as social and environmental constraints, alignment options and budgets are being pressured by location, logistical and constructability concerns.

Edged on both sides by the towering Alps, the narrow Inn valley in Austria leaves little space on the surface for new infrastructure. As well as the valley's namesake river, the 40km long Phase 1 project area accommodates 31 separate communities of private and commercial rural and urban property, existing surface rail routes and the regional section of the E60 TransEuropean highway. With precious little room on the surface, nearly all of the new rail alignment is underground, cutting into the mountains at two locations and threading its way under the river once, seven times under the motorway and ten times under existing rail lines.

Construction is also a medley of different techniques. Austria is not readily associated with soft-ground tunnelling, but some 48% of the route runs beneath the high ground water table of the valley, often within metres of the river. These conditions have demanded specialist tunnelling methods including two slurry TBM tunnels, compressed air and jet-piled support of open-face tunnel excavations, and subaqueous open-cut works. These are in addition to the two long drill+blast, and top-heading, bench and invert tunnels through the mountainsides at Brixlegg and Vomp, sections of cut-and-cover work, and just a minimum of surface work in between.

Plan of the 10 construction lots on Phase I (North & South sections) of the Lower Inn Valley double-track rail line upgrade project with their designers and contractors listed in Table 1 below.

Planning and design of the new line began in 1996. Authorization of funding in 2002 gave the green light for construction to start in August 2003. As part of the EU's current focus on the Munich-Verona section of the overall Berlin-Palermo project, planning and design of the upgrade was funded 50/50 by Austria and the EU and its €2 billion construction cost is funded 95% by Austria and 5% by the EU.

Upgrades of existing lines for the Brenner Baseline project is managed in Austria by BEG, Brenner Eisenbahn GmbH, a company of the Austrian railway company ÖBB. A separate company, Brenner Basistunnel SE (BTT), a 50/50 Austrian/Italian joint venture European stock company, is managing realisation of the estimated €6 billion Brenner Baseline tunnel. RFI, the national railway authority of Italy is managing the Southern Approach works from Verona to the base tunnel, and Deutsche Bahn (DB) in Germany is managing the Northern Approach needs from Munich to the Austrian border.

In Austria, the 40km Lower Inn Valley Phase I upgrade is a complex affair comprising more than 1,000 different procurement contracts. More than 400 of these were in progress when TunnelTalk met BEG General Manager Dipl.-Ing. Johann Herdina. At the same time, BEG is progressing planning and design of the next Inn Valley rail upgrade for the 22km section from Kundl to the German border.

Double track NATM Tunnelling

Of the 10 principal construction contracts on the current project, two were complete by end 2007, two were to be awarded in 2008 and six are currently in progress. These six represent some 28km of the total 40km alignment and correspond to more than 70% of the total construction effort progressing simultaneously (see project plan above and Table 1 below). All tunnelling and sub-surface excavation on the alignment is programmed to be complete by the end of 2008. 2008 is also the year of highest capital expenditure amounting to more than €261 million of the total €2 billion project, and following consumption of about €215 million in both 2007 and 2006. M&E installation is scheduled to start in 2008 and the new infrastructure is programmed to open in December 2012.

Mixshield TBM Assembly

Single-tube, double-track
All underground sections on the alignment are designed as single-tube, double-track structures. The drill+blast and open-face excavations have a 134m2 cross-section for a finished internal dimension of 8m high x 11.4m wide. The largest open-face excavation is a three-track overtaking section in the H5 Vomp-Terfens drill+blast tunnel and that has a 17.4m wide x 12.5m high (202m2) excavated cross section. These open-face tunnels have a primary support of shotcrete with rockbolts, dowels, lattice girders and wire mesh, with a drained PVC membrane waterproofing system behind a rebar-reinforced, cast in-situ concrete final lining of between 30-70cm thick. All shotcrete in the main excavations is wet mix with dry mix used for smaller applications such as small shafts and slope stabilisation work.

The two Herrenknecht slurry shield drives for single-tube, double-track train tracks, are 13m o.d. and are lined with 2m wide x 500mm thick, bolted and gasketed rings of steel rebar reinforced segments for a finished double track i.d. of 11.23m.

The rail line being built is a product of design principles for single-tube, double-track tunnels that prevailed in the 1980s and 1990s when France, Germany and Italy began the phase of new, dedicated high- speed rail infrastructure construction. Tunnels of large cross section and diameter were designed to accommodate tracks in both directions. These were said to have economic and operating advantages over parallel smaller diameter single-tube, single track alignments for tunnels needed to achieve the straight, level alignments needed for sustained high-speed trains. These design parameters however have since come under rigorous analysis and if planned today, alignment and construction design of the new Lower Inn Valley rail upgrade might be quite different. BEG General Manager Johann Herdina explained.

Mixshield TBM job site

Double track TBM tunnel escape shaft

"The concept of two tracks in one large tunnel has required a substantial amount of extra excavation on this project," said Herdina. "Not only for the large double-track cross-sections in these particular geological conditions, but more especially for the necessary fire-life-safety and evacuation facilities. The long Vomp-Terfens drill+blast tunnel for example has a 5.8km x 25m2 escape/service tunnel running parallel to the main tunnel with linking adits of up to 20m long at regular 500m intervals.

"On the 5.8km long Münster-Wiesing TBM tunnel there are 11 evacuation shafts at 500m intervals. These were placed as close as possible to the main tunnel alignment but in one instance the available surface space for shaft construction has required a connecting adit of 132m. These are expensive project elements. The average depth of the eleven 8m i.d. shafts is 30m and the average length of the connecting adits is 43m. The seven evacuation shafts on the 3.6km long Jenbach TBM tunnel are on average 25m deep and 50m long."

Planning today, suggested Herdina, might be based more cost effectively on an alignment of twin single- track tunnels with regular linking cross passages that would allow the parallel tube to double as the emergency escape route thus eliminating the need for separate emergency tunnels and evacuation shafts. "This would save substantial cost," he said.

There was discussion also about the cost of building and operating high-speed railway lines underground. "If new mixed-use freight and passenger railways are to be built underground, the facilities must have the most up-to-date standards in fire-life-safety equipment and systems," said Herdina. "In addition, they must be tested regularly and maintained in faultless working order to be ready for the low-probability emergency situation." These are becoming expensive long term operating costs that do not apply to surface sections of the network.

Other factors influence the final decision between surface or subsurface alignment, including important environmental concerns and land acquisition costs, but a suggested way around the dilemma, said Herdina, might be to build the new underground lines strictly for freight trains and reserve the existing largely surface alignments for passenger services. The long underground freight-only tunnels would not require the same degree of public fire-life-safety facilities and the cost effective advantages of building large double-track tunnels could be retained.

Lower Inn Valley Phase II

On long baseline tunnels where the inherent timesaving factor is needed also for high-speed passenger trains, the option would be overruled, but these and other planning, design, and operating issues are being discussed as part of future high-speed rail projects said Herdina. "We are currently studying all these issues in regard to the next 22km long phase of the Lower Inn Valley upgrade where tunnelling and underground construction is likely to be required for logistical and environmental reasons but, where more than 80% of the current 40km length of Phase I is underground, we seek to have less than 50% of the 22km Phase II in tunnel."

In the meantime, work as designed progresses on the current project.

By early 2008 and after four-and-a-half years in progress, civil work on the 40km of new twin-track railway was about 50% complete. "We have had our testing challenges," said Herdina, "but progress at present is promising and on programme to complete excavation by end 2008/early 2009 and to meet the December 2012 opening date."

Stans jet piling support program

One of the most technically demanding sections of the civil construction effort is the 2.6km long Lot H4-3 section through the village of Stans. Here the subsurface alignment runs almost directly in line and beneath the highway and surface rail tracks, and incorporates a spur tunnel for south bound traffic to the existing west bound surface rail line. Construction of this section has required four different construction methods and a total 21 phases of motorway diversion. "This section caused us the most technical challenge," said Herdina. "The highway and railway above added to the complexity of the situation and a bored tunnel was the best and yet the most complex solution."

The first 525m and last 805m lengths are constructed in open-cut work above the ground water table. Another 535m below the water table is constructed in cells of subaqueous open-cut work but it is the last 750m section beneath the highway, the railway, and the water table, that called for special attention. That special attention was provided by tunnelling under the control of compressed air and within the security of a ring of vertical pre-excavation jet-piling pre-support.

After a trial section to confirm the concept could be used and allow for safe mined tunnelling on a top heading, bench and invert sequence, site work started with mobilisation of a high-capacity grouting operation to install the vertical jet-piling in 20m x 12m long blocks. Exact drill patterns and precise packer positions achieved accurate installation of the required 2m thick ring of pre-support grouting. Angled drilling from either side of the surface railway and underneath a section of elevated highway, that could not be diverted, achieved the jet piling operation.

Stans jet piling in 3D

"The undertaking proved very successful," reported Herdina. "The ring of jet-grouting performed exceptionally well." So well in fact that the compressed-air working environment needed positive venting to compensate for very low air losses and keep the working environment fresh. "Yes it was an expensive solution but it was highly effective."

Another difficult section to complete was the last part of the 8.38km Vomp-Terfens Tunnel where drill+blast had progressed from the western portal in Terfens and in both directions from an intermediate adit. As the heading approached the breakthrough portal it suffered a collapse at the interface between the hard rock of the mountain and the zone of unstable rockfall material at its base. Recovering from the collapse and completing the tunnel to breakthrough proved exasperatingly slow. It took 19 months and huge volumes of grout, injected from the surface and from within the tunnel heading, to complete the last 180m of top heading, bench and invert.

Chronology of the Berlin to Palermo number one priority project in the EU's TransEuropean Transportation Networks strategy (TEN-T)

July 1986

Germany, Austria and Italy agree a feasibility study of the Brenner Baseline Tunnel as the crucial link in the 2,400km long line.

April 1989

Feasibility study approved and Brenner Base Tunnel is declared the base for all further planning of associated feeder line upgrades.

October 1993

Presentation of feasibility studies for the Northern and Southern access line upgrades.

December 1994

Berlin-Palermo upgrade is selected number 1 of the 14 TEN priority projects.

January 1996

BEG company founded to manage construction of project works in Austria.

September 1997

Austria approves the budget for the Kundl - Baumkirchen upgrade. Planning is funded 50/50 by Austria and the EU; construction is funded 95% by Austria and 5% from the EU.

April 1999

Construction of an exploratory tunnel starts for Brixlegg Tunnel.

April 2002

Authorization for start of the project's main line construction.

August and October 2003

Start of the first two of 10 main construction contracts.

2004

BBT, a 50/50 European Stock company between Austria and Italy, is formed to manage construction of the Brenner Baseline Tunnel.

2008

Construction of a €78.9 million, 10.5km long x 6.3m diameter TBM-driven exploratory tunnel for the Baseline Tunnel begins from the Italian side at Aicha. The contract consortium includes Pizzarotti (Italy), Bilfinger Berger (Germany), Alpine Mayreder (Austria), Beton-und Monierbau (Austria), Jaeger (Switzerland), and Seli (Italy).

December 2012

Trains start to run on the first section of the new Lower Inn Valley railway.

2022

Current target for Brenner Baseline Tunnel to open.

Stans jet piling in situ

To conclude the meeting with TunnelTalk, Herdina explained that because of the various challenges the project's original civil construction estimate of 2003 had increased by 15%. Time wise, he said that delays on different contracts had pushed forward the opening date by a year, but that work was currently on schedule to meet the revised December 2012 opening date.

Meanwhile, planning and design of the Lower Inn Valley Phase II upgrade is progressing towards a start of construction in the second half of 2008. When complete, Phases I and II of new rail through the Lower Inn Valley will contribute in no small measure to success of the Berlin-Palermo achievement.

Sequence of subacquious cut-and-cover excavation

Table 1. Details of the 10 principal construction lots

Contract	Principal designers	Contractor JV	Contract price	Start	End
Lot H1 Kundl - Radfeld Length - 5,329m Upgrade of existing surface track and construction of 900m	Spirk & Partner Pauser ZT- GmbH Obermeyer ILF GTH - Geotechnik Hammer ISF	To let in 2008	-	Jul '08	Jul '10
Lot H2-2 Radfeld Mitte Length - 2,390m 790m of open-cut subaqueous excavation and 1,600m of conventional mined tunnelling	Geoconsult/Baumann+ Obholzer Spirk & Partner/Obermeyer D2 Consult/SEIB	To let in 2008	-	Mar '08	Apr '11
Lot H2-1 Radfeld - Brixlegg Length - 4,345m Conventional tunnel Topheading, bench, invert Shotcrete primary lining PVC waterproofing system and in-situ concrete final lining	ILF/Vossing ILF	Porr/Bilfinger Berger Hinteregger/ÖSTU STETTIN	€ 66 million	Jul '04	Dec '06
Lot H3-4 Münster - Weising Length - 5,746m 13m slurry shield tunnel 11 emergency escape shafts Segmentally lined	Spiekermann Obermeyer ibk/Metz & Partner D2 Consult/Oksakowski	Porr/Max Bogl JV	€ 154 million	Apr '06	Dec '10
Lot H3-6 Tiergarten Tunnel Length - 671m	Geoconsult Obermeyer ibk/Metz & Partner D2 Consult/Oksakowski IPH	Beton-und Monierbau/ Alpine Mayreder/ Jäger JV	€ 14 million	May '07	Aug '08
Lot H8 Jenbach/Stans Length - 5,182m 13m slurry shield tunnel 7 emergency escape shafts Segmentally lined	Obermeyer	Strabag/Hochtief/Züblin JV	€ 150 million	Jul '06	Aug '10
Lot H4-3 Stans/Fiecht Length - 2,615m 4 construction methods benearth existing railway and E60 highway	Geoconsult / ILF Grund-Pfahl-und Sonderbau JV	Alpine Mayreder/	€ 104 million	Aug '05	Feb '10
Lot H5 Vomp-Terfens Length - 8,380m Conventional tunnelling	Geoconsult Geodata/AVD; ste.p Oksakowski/D2 Consult	Strabag/Züblin/Hochtief JV	€ 187 million	Aug '03	Dec '08
Lot H6 Terfens Gallery Length - 1,300m Covered twin-track avalanche protection gallery	Baumann+Obholzer/ Geoconsult; ILF Geodata/AVD ste.p	Strabag	€ 19 million	Oct '03	May '07
Lot H7 Fritzens/Baumkirchen Length - 5,315m 3,940m of topheading, bench, invert tunnelling using horizontal pipe-umbrella pre-support, face nailing and compressed air between open-cut, subaqueous, and surface work	Geoconsult ste.p Obermeyer/GEC/Spirk & Partners IBPA IPH HBPM	Strabag/Hochtief/Züblin JV	€ 139 million	Feb '05	Dec '09

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