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State border tunnel Füssen, BAB A7

1. Task definition

The A 7 federal freeway is one of the most important German trunk road links. With currently 945.6 km it is the longest freeway in Germany. In the Bavarian section Würzburg - Ulm - Kempten - Füssen, the A 7 currently ends northeast of Nesselwang with a temporary connection to the district road OAL 1.

On the Austrian side, the Fernpass road B 314 provides the most important traffic connection between the western parts of Tyrol and the Federal Republic of Germany. With a total length of 55.7 km, its main importance lies in the tourist sector as a feeder road to the alpine recreation areas. In summer, it also provides an important connection to Italy via the Brenner Pass and the Reschen Pass.

The A 7 federal highway and the B 314 Fernpass road are linked at the federal border west of Füssen to form an efficient cross-border traffic link. The section from the provisional end of the freeway near Nesselwang to the connection to the Reutte northern bypass forms the missing final section. The centerpiece of this gap in the highway network, which is around 22 km long in total, is the Füssen border tunnel. Of its total length (1284 m), 932 m are on German territory, 352 m of the tunnel tube are in the Republic of Austria.

The first planning ideas date back to the late 1960s on both the German and Austrian sides.

The planning envisaged a tunnel tube with two-way traffic. The roadway consists of two lanes of 3.75 m each and two shoulder lanes of 0.50 m each. The width of the roadway between the curbs is thus 8.50 meters. Emergency walkways with a width of 1.0 m are arranged on both sides. The cross-section has the dimensions of cross-section type 12T.

The clearance height is 4.70 m in the area of the travel space. In addition to the clearance, a construction tolerance of 5 cm was taken into account.

The tube first rises from the north to the south portal with a gradient of 0.5% (approx. 370 m) and the rest of the way with 2.0%. The radius of curvature of the trough is 40.000 m. The height difference of the tunnel portals is 18 m.

The two breakdown bays north and south are located at the third points, each with parking lanes about 40 m long on both sides. The width of the side parking lanes is 2.50 m and 2.60 m respectively. Here there is a turning possibility for cars and small trucks (turning circle diameter smaller than 13.50 m).

The sidewalks in the area of the breakdown bays are 0.85 m wide; the clearance height in the area of the parking lane is 4.50 m.

A 434 m long escape tunnel leads from the north breakdown bay to the open air approx. 40 m west of the north portal. The cross-section is dimensioned so that small rescue vehicles can drive through it.

2. Structural design

2.1 Geological conditions

The project area is located in the so-called Falkenstein range, an east-west trending mountain range of the Northern Limestone Alps. The 1284 m long tunnel running in north-south direction can be roughly divided into three main sections in terms of construction:

Section north (Main dolomite in the Burkenbichlberg)

In the Burkenbichl, the maximum overburden is 160m. The main dolomite, which is largely stable, exhibits clear stratification and fracturing that is almost parallel to the site. Due to the high rock strength, the rock could only be excavated by blasting. Numerous tectonic faults (fractures) running at an acute angle to the tunnel axis brought in this area partly considerable amounts of mountain water (5-10 l/s). At the transition to the Raibl strata, fracturing and mountain water flow increase significantly.

Middle section (Raibl strata and quaternary section in Faulenbach valley)

The Faulenbach Valley, which is designated as a landscape conservation area, is crossed relatively close to the surface - with a minimum cover of 20 m above the tunnel ridge.

The Raibl strata encountered in the Faulenbach Valley consist of a colorful alternating sequence of limestones, dolomites, sandstones and clay siltstones, most of which can be loosened mechanically with the aid of loosening blasts. From station 580, they are interrupted on a tunnel section of approx. 40 m by a sequence of loose sediments originally called "Quaternary gully".

However, geological findings obtained in the course of the construction work have not confirmed the originally assumed channel structure of this sequence. Rather, it is a sinkhole formed by gypsum leaching in the subsoil, which had been filled with unconsolidated sediments in the course of time. Both the northern Raibl strata and parts of the main dolomite had obviously subsided into this sinkhole in the course of time. This resulted in extensive dissection of the rock into floes and debris embedded in a variably dense, clayey, water-bearing matrix. This resulted in extremely difficult geotechnical conditions for tunnel driving.

South section (Wetterstein limestone and partner layers in the Vilser Berg)

In the Vilser Berg, at a maximum overburden of 210 m, the national border to Austria is crossed. The Wetterstein limestone is largely massive and stable. The mountain water flow (individual inflows of up to 15 l/s) is mostly linked to karst systems, which are increasingly encountered in the area of healed tectonic faults.

2.2 Supporting structure, sealing

The geometric shape of the tunnel cross-section is adapted to the rock mechanical properties of the rock mass and meets the tunnel construction requirements.

Two types of construction were used in the invert area. In the area of the Faulenbach valley, a closed invert with a normal and shallow invert arch was used.

In the adjoining areas on both sides, there is no invert closure.

The tunnel design was based on a double-shell construction method (shotcrete protection / concrete inner lining).

In principle, two different waterproofing systems were used:

Umbrella sealing

The "umbrella waterproofing" spans the ridges to the flow bottom of the elm drains and consists of a layer of geotextile and a 2 mm thick waterproofing membrane made of flexible polyolefins (FPO). This waterproofing system was used in the northern and southern construction sections, where drainage pipes are installed both along the elms and in the bottom.

Pressure-tight all-round waterproofing

The "pressure-tight all-round sealing" system is used in the Faulenbach Valley section, where the tunnel is not drained. Here, the tunnel is designed to be pressure-tight over a length of 276 m (up to 50 m water column) so as not to adversely affect the water balance in the landscape conservation area above and also the Notburga healing spring in Bad Faulenbach.

At the Füssen border tunnel, the "compact method" known from power plant construction was used for the first time in traffic tunnel construction. Here, a 3 mm thick waterproofing membrane made of FPO - without geotextile backing - is laid directly on the waterproofing support. On the uphill side, "fleece barriers" are used to create defined bulkhead fields with a size of approx. 80-90 m2 , which are backed with cement suspension over the entire surface via injection nozzles after concreting the invert arch or the inner shell.

The cement backfill closes the gap between the shotcrete and the waterproofing membrane so that it is watertight. This means that there is no longer any possibility of the mine water flowing along the waterproofing from the pressure-tight area into the shield waterproofing area. Preventing the longitudinal flow of mountain water is the decisive advantage of the compact method over systems with fleece backing.

At the portals and in the breakdown bays, the inner shell thickness is 30 cm, in the shield sealing areas 25 cm and in the pressure-tight area 40-50 cm, depending on the height of the assumed mountain water level. Only 3 portal blocks each in the north and south as well as the 24 concreting sections of the pressure-tight area were reinforced.

The roadway is drained via a slotted channel. Approximately every 50 m, the roadway water is discharged via a siphon into a test shaft. The collection pipe discharges the roadway water completely to the north to a collection basin west of the north portal. The basin (102 m3) is kept empty during normal operation by two alternating pumps.

The mountain water (spring water) is collected in a completely separate pipe system (elm or base course drainage) and discharged into the mossy areas north of the tunnel after continuous volume measurement. For the control and cleaning of the drainages, flushing shafts are arranged in corresponding niches approximately every 50 m in the tunnel.

No mountain water is discharged from the pressure-tight tunnel section.

2.3 Operating facilities, equipment

Each direction has two breakdown bays arranged opposite each other.

The tunnel is equipped with a passageway lighting system divided into six sections and with approximately 360 m long entrance lights on both sides.

Two jet fans are installed in the tunnel at a distance of about 300 m from each of the two portals, the blowing direction of which can be reversed (longitudinal ventilation). The escape tunnel is also equipped with fans.

In normal operation, the ventilation is automatically controlled according to the prevailing flow direction, CO content and air turbidity.

The installed light signal systems and variable message signs can be used to block the respective directions of travel or operate in alternating traffic.

The occupancy of the tunnel (number of vehicles in the tunnel) is recorded by the central control system.

The tunnel is supplied with power from both the south and the north from the public medium-voltage grid, thus ensuring a high level of supply reliability.

From the tunnel control room in the Memmingen highway maintenance office, the entire tunnel as well as the pre-gantry areas can be remotely monitored by a television system with 12 cameras.

In addition to the manual fire alarms in the emergency call niches and at the portals, fire alarms are sent to the tunnel control room via an automatic line fire alarm system.

The tunnel is equipped with a radio system for fire departments with additional working radio, police / gendarmerie, operating service of the highway maintenance department with appropriate cross-border coupling possibilities. The rescue services share the channels of the fire departments.

The tunnel is supplied from two operational buildings.

A total of eight fire extinguishing niches are located in the tunnel at intervals of 120 - 150 m on the eastern side. Two hand-held fire extinguishers are located in each of the opposite emergency niches.

2.4 Construction method

Based on the geological forecasts, it was expected that the tunnel could be excavated conventionally using the shotcrete construction method in drilling and blasting operations, with the exception of short sections in the Faulenbach valley. For reasons of occupational safety, the contractor's concept of full excavation was discouraged and the tunnel was excavated from Station 50 onwards using the calotte and bench driving method.

Due to water law requirements, a blasting method that was as gentle as possible on the rock was necessary in all driving areas.

In blasting, average daily advance rates of 10 m were achieved; the bench followed the calotte at a distance of approx. 50 m. The tunnel was then excavated using the blasting method.

The portal areas including the service buildings were constructed using the cut-and-cover method.

3. Construction execution

The contract for construction was awarded on the basis of the tendered design.

Construction officially began with the tunnel cut at the north portal at the beginning of December 1995.

The tunnel was excavated in a north-south direction. The breakthrough into the Vilstal took place on 17.09.1997.

Excavation was initially carried out as a full excavation and then separately in calotte and bench partial excavations.

The beginning of the Raibl strata was expected from station 530. On March 6, 1996, in the course of exploratory drilling at Station 480, the largest volume of mine water to date was shaken out at about 20 1/s. The excavation was then stopped. As a result, driving was stopped and horizontal core drilling was ordered for further preliminary exploration. Shortly after the start of core drilling operations, a sudden and unexpected water intrusion occurred on March 9, 1996, with an initial surge estimated at 400 1/s. By March 15, this water ingress was almost completely prevented by initial advance injection measures.

Further driving was carried out with systematic advance injection.

The tunnel received a double-shell lining, an outer shell as safety shoring and an inner shell as concrete lining.

This was followed by the construction of the drainage facilities and the concrete roadway.

Installation and trial runs of the operating and safety equipment completed the construction measures.

The new section of the A7 freeway was opened to traffic in July 1999.

4. Literature

[1] Autobahndirektion Südbayern, München und Landesbaudirektion, Straßenbau, Innsbruck: Dokumentation BAB A 7, Fernpass Straße B 314 Abschnitt Füssen bis Reutte-Nord, Grenztunnel Füssen

[2] Arge Grenztunnel Füssen, ÖSTU-Stettin / Gebr. Haider, Leoben: BAB A 7 Würzburg - Ulm - Füssen - (Reutte) B 314 Fernpass-Straße, Grenztunnel Füssen Technische Informationsschrift Tunnelbau

[3] Autobahndirektion Südbayern, Dienststelle Kempten: Grenztunnel Füssen, Bestandsplane, Photodokumentation



  • Country: Germany/Austria
  • Region: Bayern, Tirol
  • Tunnel utilization: Traffic
  • Type of utilization: Road tunnel
  • Client: Bundesrepublik Deutschland, Bundesministerium für Verkehr, Bau und Wohnungswesen Republik Österreich, Bundesministerium für wirtschaftliche Angelegenheiten
  • Consulting Engineer: Ingenieurgemeinschaft Lässer-Feizlmayr
  • Contractor: Östu-Stettin Hoch- und Tiefbau GmbH, Gebr. Haider
  • Main construction method: Trenchless
  • Type of excavation: Drill-and-blast
  • Lining: In-situ concrete
  • No. of tubes: 1
  • Tunnel total length: 1,284 m (Germany: 932 m, Austria 352 m)
  • Contract Volume: 61 miil. DM
  • Construction start/end: December 1995 till July 1999