Brenner Base Tunnel: Stage reached by Construction

Currently the exploratory tunnel sections are being produced for the Brenner Base Tunnel project and the guide design for the main tunnel is to be embarked on in the near future. The following report provides an overview pertaining to the stage reached by construction.

1 The TEN Axis from Berlin to Palermo
The trans-border European priority scheme TEN Project No. 1 represents a roughly 2,200 km long high-speed railway route between Berlin/D and Palermo/I. Between Berlin and Naples/I ¾ of the 1,600 km section is already under construction or in operation. The southern section between Verona and Naples started operating in its entirety in December 2009 when the part-section between Bologna and Florence was finished. Five priority sections were defined from Verona to Franzensfeste. These include the access to Verona and the underground bypassing of Trient and Rovereto. The first geological studies, the feasibility study and the route alignment were completed for the section in the Tyrolean lowland. The city of Bozen is also to be bypassed by a roughly 14 km long tunnel. The section between Waidbruck/Ponte Garde-na and Franzensfeste/Fortezza is an important one. There the existing route possesses a 23 ‰ gradient.
The 55 km long Brenner Base Tunnel [1] starts at Fran-zensfeste Station. The new rail route joins up with the existing Innsbruck bypass thus creating a 62.5 km long underground tunnel link. The bypass at Innsbruck joins up with the 41 km long Lower Inn Valley route between Baumkirchen and Kundl, which is scheduled to be completed and in operation by 2012.
A programme of action was signed by all 3 member states on May 18th, 2009 to support time-related development and to push through the relevant political measures for transferring traffic from road to rail. The 3 member states and the 5 affected regions and the railway operators are committed to putting this programme into practice according to schedule (Fig. 1).

2 Current Knowledge of the Geology – Hydrogeology
In geographical terms the entire length of the planned Brenner Base Tunnel runs through the central area of the eastern Alps. However, geologically speaking it passes through the ascending arched centre of the collision zone between the European and Adriatic (African)   plates, which are present in the form of a number of nappes lying on top of each other. In the process the tunnel crosses the Tauern Window, which provides an insight into the deeper crust zone of the eastern Alps on account of the arched effect that was referred to. From north to south along the entire tunnel route the major tectonic units are the Unterostalpin, the Pen-ninic nappes of the Tauern Window, a narrow zone with Oberostalpin and tertiary intrusive rocks in the S-shape of the Tauern Window and the Südalpin (Fig. 2).
Let us now consider the straight route alignment of the tunnel from Innsbruck (km 0) to Franzensfeste (km 55).

Innsbruck Quartz Phyllite to km 14
– A new evacuation tunnel with a length of some 5.3 km is being built to the north of the existing bypass tunnel in the Innsbruck quartz phyllite zone.
– 0 to 14  km: Unterostalpin/Innnsbruck quartz phyllite zone
In similar fashion to the Inntal Tunnel crumbling rock behaviour is expected outside fault zones, which transforms to shear failure as the overburden increases and to pressure phenomena when nearing the Tauern Window. The rock behaviour is decisively influenced by the fault zones. The shallow transverse faults play only a subordinate role. The Wipp normal faults running at an acute-angle and the presumed thick Ahrental fault, the continuation towards the west of the massive Lavierental fault penetrated by the Inntal Tunnel are critical.
There is no significant flow system in the Innsbruck quartz phyllite nappe. Higher permeabilities can only occur in the main faults, however only less significant flow systems are linked with them.

14 to 28.5 km
– 14 to 19  km: North marginal zone of the Tauern Window
The conditions vary substantially; they are friable and tend towards shear failure. The layers containing anhydrite are restricted to a few cm and thus unimportant. However major blocks of anhydrite, dolomite etc. cannot be precluded. Apart from the presumed 50  m thick Mislkopf Tauern northern marginal fault the acute-angled faults of the north-south running normal faults result in sustained pressure phenomena.
– 19 to 28.5  km: Glockner nappe
Slightly squeezing rock is to be expected in the southern zone when encountering black phyllites to an increasing extent, whereas no high swelling pressures will occur in the anhydrites. Hydrogeologically speaking the Innsbruck phyllite nappe transforms to become the Glockner nappe through hydrogeologically insignificant, ductile tectonic contact. The Glock-ner nappe constitutes Bündner slates, which are formed from slates containing varying degrees of lime. Within the slates, dolomites, quartzites, anhydrites, grey wackes and serizite slates are to be found.
The permeabilities associated with the lime-rich Bündner slates are low in the absence of solution phenomena. As far as the Bündner slates that are low in lime are concerned they are associated with slight or very slight permeability. Permeabi-lities in the main fault zones can experience a considerable increase. This can occur in the lime-rich Bündner slates as areas with chemical solutions can form in zones affected by damage. The existence of significant flow systems at tunnel level in the zone where such units are penetrated can be precluded.
28.5 to 36 km
– 28.5 to 30.3 km: Lower slate mantle to the north of the Tux central gneiss core. This section is characterised by alternating rock conditions. Shear failure and deep-lying deconsolidation as well as pronounced ingressing water are to be reckoned with. Locally anhydrite elution and material discharge can occur, which result in crumbling rock. – 30.3 to 36  km: Central gneiss – Brenner boundary
The central gneiss can largely be regarded as being stable; however, joint plane solutions are to be reckoned with. Pressure phenomena are expected in the Olper Faults area; otherwise the faults will probably not greatly influence the rock behaviour.
Towards the south the Bündner slates of the Glockner nappe pass through an imbricated zone to form the lower slate mantel. This unit starting from the top consists of sedimentary, permo-mesozoic covering rocks, which were formed from various layers of slates, meta-carbonates and subsidiary evaporitic rocks and central gneiss. The sedimentary coverings possess variable permeability characteristics and can also embrace flow systems. No flow systems are associated with the central gneiss in the Brenner area, as it possesses low permeability. Average permeabilities only occur in fault zones.

36 to 40.5 km
– 35.9 to 37.2  km: Lower slate mantel of the Pfitsch Synform
The intermittent bedding of the types of rock and their variability make it more difficult to characterise the rock behaviour, which is largely governed by shear failure. The transverse fault zones reinforce possible shear failure. – 37.2 to 40.5  km: Glockner nappe of the Pfitsch Synform
The Bündner slates reveal varying behaviour, ranging from structurally-related cavities to extreme squeezing behaviour. This behaviour appears to be confined to short areas and the fault zones.
Hydrogeologically speaking there is no significant flow system in the gneisses between the Brenner and the Pfitschertal valley. A more important flow system could possible be located on the boundary between the gneiss and the covering Glockner nappe (Bündner slate).

40.5 to 47.5 km
– 40.4 to 43  km: Lower slate mantel/central gneiss
Structurally-related cavities can occur in this section.
– 43 to 45.4  km: The Bündner slates display the same behaviour to the south of the high arch as to the south of it; the higher stress level can lead to stronger pressure phenomena.
– 45.4 to 47.5  km: Oberostalpin Crystalline
In the Ostalpin structurally-related cavities and cavity-like strength failure as well as a major fault are anticipated.
To the south of the Pfitscher-tal the hydrogeological complexes are folded around the large Tulver-Senges Antiform. The sections consist of the Bündner slates of the Glockner nappe, within which significant flow systems are not expected.

47.5 to 48.2 km: Periadriatic Fault Zone
– 47.5 to 48.2  km: Mauls tonalitic Lamella/Periadriatic Fault Zone
The existing findings obtained by drilling at Mauls reveal that numerous faults result in a geotechnically tricky area, which in addition is exacerbated through ingressing water.

48.2 to 55 km
– 46.2 to 55: Brixner Granite
Brixner Granite represents a stable relatively hard rock, which was also confirmed by the Aicha-Mauls exploratory tunnel. However, individual deconsolidated sectors are possible.

3 Stage reached by the Brenner Base Tunnel
3.1 Essential Criteria of the Project
Together with the Innsbruck bypass the 62.7 km Brenner Base Tunnel is the world’s longest underground rail link. It consists of 2 bores located alongside one another with an internal diameter of roughly 8 m and set 70 m apart. The exploratory tunnel with a smaller diameter, which is for advance investigation purposes and for subsequent drainage, is to be found underneath the main tunnels (Fig. 3). The most important features of the Brenner Base Tunnel are:
– length: 55 + 6.5 = 62.5 km
– longitudinal gradient: 5.0 to 6.7 ‰
– apex height of the Base Tunnel: 795 m ASL
– net cross-section of the main bores: approx. 43 m²
– distance between cross-passages: 300 m.
An exploratory tunnel is being driven centrally approx. 12 m below the main bores. It possesses an internal diameter of some 5 m. It mainly serves for examining the geology along the selected route. At a later stage it will be used for drainage purposes, something which makes perfect sense in technical terms as it will always be possible to undertake maintenance in the drainage tunnel without affecting rail services. Altogether 3 multi function stations set some 20 km apart are foreseen namely at the Innsbruck bypass, at St. Jodok (south of Steinach) and at Trens (to the north of Mauls). These multi function stations will be opened up by a negotiable access tunnel.
A 25 kV – 50 Hz traction system is to be installed in the Brenner Base Tunnel in accordance with the TSI Guideline. For the Brenner Base Tunnel and all newly constructed sections of the Brenner Axis the ERTMS – Level 2 (European Rail Traffic Management System) was chosen as the train safety system in keeping with the TSI CCS. The traffic control centre will be set up at Innsbruck; an emergency centre at Verona or Bologna (Fig. 4).

3.2 Approval
The preliminary project was drafted in 2002 and the detailed scheme and environmental compatibility project passed on to the authorities in Italy and Austria for their approval in March 2008. In Austria construction approval in keeping with the Austrian Railway Act and further permits were awarded by the Federal Ministry for Transport, Innovation and Tech-nology on April 15th, 2009. Additional permits relating to waterways, conservation and landfills were granted by the governor of Tyrol. Appeals or complaints were lodged by certain groups or organisations against individual permits. Some of these were rejected but others are still in the process of being dealt with.
In Austria the project is being financed by the ÖBB Infrastructure Framework Plan (agreement reached on July 24th, 2009 on the Framework Plan 2009–2014). The relevant legal regulations came into force on August 19th, 2009 in the form of the § 42 Bundesbahngesetz, Novelle BGBI. I Nr. 95/2009.
The documents tabled for the entire project were approved in Italy on August 31st, 2009 by the Interministerial Committee for Economic Planning (CIPE). The requirements relating to tunnel safety were also regulated and concluded in accordance with the guidelines. With the CIPE resolution and the Finance Act 2010 No. 191 from December 23rd Italy has committed itself to financing the entire construction project.

3.3 Tunnelling at the Brenner Base Tunnel
3.3.1 Building the exploratory Tunnel Sections
An exploratory tunnel, which runs at a greater depth, is being built in advance for the Brenner Base Tunnel. The findings thus obtained through tunnel monitoring will flow towards assessing the excavation and supporting methods alongside experience [2]. Since August 2007 work has been progressing on the 10.5 km long Aicha–Mauls exploratory tunnel. 6.5 km has already been bored through Brixner Granite using a double shield machine and segmental support. The TBM possesses 6.3 m diameter. The segments (4 elements and a keystone) provided with reinforcement matting have 20 cm wall thickness and are 1.5 m wide. The excavated material uncovered after some 500 m is an extremely hard granite with Los Angeles values varying from 15 to 20. From the point joining up with the Mauls access tunnel towards the north in the direction of the Periadriatic Seam the 700 m exploratory tunnel is also being driven by conventional means. The exploratory tunnel has a 31 m² cross-section and a longitudinal gradient of about 0.5 %.
The next contract section concerns the penetration of the roughly 1,100 m long Periadriatic Seam, where initially the rock pressure and possible ingressing water will be investigated using horizontal drilling. The 1.8 km long access tunnel at Mauls with 8.5 % longitudinal gradient has already been completed using drill+blast. Towards this end a 92 m² cross-section was produced, which is needed for the construction logistics. Supporting was executed with a fibre-reinforced shotcrete and by means of anchors (Superswellex) in some sections. 5 m per day was the average rate of advance accomplished by conventional means. Water inflows in this section were considerably more restricted than predicted amounting to about 5 l/s. Work on the 400 m long Unterplattner Tunnel, which is close to the surface, where the conveyor systems are to run between the Aicha site and the Hinterrigger dump, was also concluded. Work on the Innsbruck– Ahrental exploratory tunnel began on December 4th, 2009. After constructing the water protection facilities drill+blast will be used to construct the first roughly 290  m long section in the Sillschlucht near Inns-bruck. Over the first 30 m with crumbling rock, steel lances were installed at the face securing the working area in advance to restrict overbreak and protect the crew. Afterwards the 5.4 km Innsbruck–Ahrental exploratory tunnel and the 2.42 km Ahrental access tunnel are to be produced by means of drill+blast. The next sections of the exploratory tunnel programme relate to the Wolf area, the construction site area and the Wolf access tunnel are to be built in addition to 2 access tunnels close to the surface (slip road from the motorway; 900 m long Saxen Tunnel and access road to the Padastertal dump; 500 m long Padaster Tunnel).

3.3.2 Monitoring
An extensive monitoring programme was developed or prescribed by the authorities for observing the rock formations and to secure verification for the exploratory tunnel for the Brenner Base Tunnel. Windows or entire segmental rings were left open roughly every 250 m along the exploratory tunnel Aicha–Mauls in order to ensure that any structural changes were visible to the naked eye. The deformation measurements are partly integrated in the segments (Aicha–Mauls) or the shotcrete shell (Innsbruck–Ahrental). In concept this monitoring programme serves the observation of radial deformations following excavation as well as later when the main tunnels are being built (Fig. 5).
The stresses and deformations established by means of a non-linear calculation show that the extreme value of the stress (sxx) amounts to roughly 1.9 MPa. This value occurs in the tunnel shell close to the connection between the right segment and the base segment. The vertical stress reaches a maximum value of 4.3 MPa to the side of the tunnel shell. The maximum vertical deformation in the roof amounts to around 3 mm. The horizontal deformation is extremely slight (Table 1). The behaviour of the segments under increasing load reveals a relatively linear increase with a defined plastic zone. According to current investigations of the concrete compressive strength for the ready-cast segments the cylinder compressive strength is in excess of 50 MPa. Essential for monitoring is the proper processing of the data as well as the interpretation of the results with regard to the safety of the support measures [5]. In principle the measured deformations represent the state of the effect. This is opposed by the resistance of the support elements (segments or shotcrete). As deformation-relevant characteristics are concerned here, the measured deformations „uMon“ are compared with the effect of the maximum deformations „uR, max“ of the support (determined by analysis or experimentally).
Given linear behaviour the maximum deformation of the support element (concrete) can be calculated in simplified form as follows [4, 6, 7]:   
To estimate the required safety a simplified probalistic assessment is executed. In the process the effect represents a normal distribution basis variable and the support resistance a lognormal one.
Taking scatter variables into consideration the safety index (similar to the safety theory) can be determined (Fig. 6):

R – S = Z[2]
The average value and the standard deviation for the basis variables are now calculated. In this way the safety index ß can be worked out by means of the following formulation (Fig. 7).


The static characteristic values of the lognormal distribution value of the support resistance can be worked out in simplified form:   



The orders of magnitude shown in Table 2 are selected for stochastic modelling based on a number of assessments.
As this consideration of limit values relates to deformation criteria, 3 assessments are proposed depending on the case of application and further development of the support (Table 3).
The aim is to improve prognoses by continuous measurements so that the risks during construction and in turn the costs as well can remain calculable.
3.3.3 Main Tunnel
Enormous knowledge has been acquired for the Brenner Base Tunnel project through a very extensive geological and hydrogeological drilling programme in excess of 25,000 m. Furthermore these recognitions have been further enriched through the results obtained from the exploratory tunnel. Towards this end the geologically tricky sections are first penetrated by the exploratory tunnel so that these findings can be included in the data for constructing the main tunnel. As things appear at present roughly 2/3rd of the main tunnel will be driven by mechanised means using tunnel boring machines and 1/3rd conventionally with drill+blast. Measures designed to improve the rock and grouting can be executed both in advance from the exploratory tunnel as well as from the main tunnel. The rock can be improved by high-pressure injections using special cement suspension solutions and possible ingressing water reduced. These techniques can be deployed either to secure the face during a tool change on the tunnel boring machines as well as for tunnel sections with poorer quality rock and a high inrush of water. Such measures can be utilised for the Brenner Base Tunnel in certain sections such as for the Inns-bruck quartz phyllite, the Hochstegen Limes – Venntal or the Periadriatic Seam at Mauls.
The process adopted for rock improvement measures can be summarised as follows:
– Rough delimitation of the fault zones by reflection seismics – Advance drilling using core drilling or percussion drilling possibly protected by a preventer
– Reduction of inflowing water via advance grouting (umbrellas) with overlapping
– Penetrating the fault zone protected by the umbrella.
Reflection seismics is currently also being applied for the Aicha–Mauls exploratory tunnel. The outcome of such measurements must however always be carefully interpreted and rounded off with advance drilling if need be. These recognitions were also obtained at the fault zone at km 6.1 for the Aicha – Mauls exploratory tunnel. The production of the main tunnel takes place during Phase III, which the BBT SE has still not been commissioned with. The aim is to commence the planning programme for the main tunnel in 2010.

3.4 Material Logistics
The total amount of the tunnel excavation material produced by the Brenner Base Tunnel including the quantities from the exploratory tunnel programme will constitute around 15.5 mill. m³ in compacted state. The dump sites will be set up immediately alongside the access tunnels; these will in some cases be linked with their own transport tunnel – as is the case in the Padastertal. Thanks to such optimisation transport routes can be reduced and the material removed without having to use lengthy routes via public roads. The excavated material was forecast on the basis of the construction logistical investigations and assessed in 4 lithological classes. Each of these 4 classes was divided into corresponding utilisability sub-classes – namely material for concrete aggregates, fill material and excavated material with no further use. Only class A was excluded for calculating the dumps (Fig. 8). The following utilisability classes were defined:
– Utilisability class A: high-grade material suitable for concrete aggregates
– Utilisability class B: material for embankment fills and backfilling
– Utilisability class C: material with no further use and to be dumped on site.

4 Summary
The “Brenner Base Tunnel is coming” – this is what the EU Coordinator Karel Van Miert, who unfortunately died as a result of a fatal accident on June 22nd, 2009, postulated on June 16th, 2009. Currently the exploratory sections are being produced; in the near future we shall commence on a superordinated guide design for the main tunnel and then proceed with building it. The BBT SE is desirous of creating a scientific asset thanks to this infrastructure facility. On June 5th, 2009 a framework agreement was drawn up with 7 universities. In this connection new technologies are to be scientifically supported by the universities with economic, social and ecological themes being tackled. Through intensive exchange findings obtained from the surrounding tunnels will be integrated.


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