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Jagdberg Tunnel - BAB A4

1. General

1.1 Task

In the course of the six-lane expansion of the federal freeway A4 Eisenach - Görlitz, section AS Magdala - AS Jena/ Göschwitz, traffic project German Unity No. 15, the construction of the tunnel Jagdberg took place. The project of the entire section Leutratal was assigned by the Free State of Thuringia to DEGES Deutsche Einheit Fernstraßenplanungs- und -bau GmbH for planning and construction.

The tunnel is named after the 288 m high Jagdberg, which rises between Jena-Göschwitz and the east portal of the tunnel. To the east and west of the Leutra valley, six lanes of the highway have already been under traffic for some time. The deferred expansion section in the Leutra Valley had considerable traffic deficiencies and no longer complied with today's regulations. Extreme gradients, unfavorable visibility conditions, insufficient curve radii and a predominant lack of hard shoulders led to an above-average frequency of accidents on this section of the highway. In addition, there were high noise and pollution levels for the neighboring villages and nature reserves against the background of the considerably increased traffic load since reunification. Due to the complicated topographical and ecological boundary conditions, elaborate variant studies of the route were necessary in order to determine the optimum solution taking into account traffic safety, regional planning, ecology and economic efficiency. The new route deviates from the old route east of the Magdala junction, runs approx. 1.3 km north of the existing route and turns back to the existing route immediately west of the Jena-Göschwitz junction. The maximum longitudinal gradient was reduced from 6% to 3.7% as a result of the new alignment. In the tunnel, the longitudinal gradient is a constant 2.95%. The standard cross-section of the new highway is RQ 35.5 with six lanes and two hard shoulders.

1.2 Nature conservation

The entire Leutra Valley represents a highly sensitive natural area worthy of protection. In the area is the nature reserve "Leutratal", which is one of the most important distribution areas of rare orchids in Germany with 27 proven orchid species. Furthermore, an FFH area and an EU bird sanctuary are located in this valley. The new construction of the Jagdberg Tunnel and the simultaneous dismantling of the old route with complete removal of the traffic will provide lasting relief for these protected areas. The separating effect of the old route in the ecologically important natural area will be eliminated.

1.3 Geology

The tunnel crosses several geological layers from west to east (Lower Muschelkalk, Upper, Middle and Lower Röt) and a fault system, the so-called Leutra fault. The limestone or marl limestones are predominantly rock solid. Only in the approach area at the west portal and in the fault zone is the rock partly deconsolidated. In the area of the Mittlerer Röt, gypsum inclusions and rock water attacking the concrete were found.

1.4 Structure design

The design of the tunnel structure is essentially determined by the integration of the portals into the landscape. Both portals have natural stone cladding in the entrance area, which takes up and continues the look of the natural stone cladding of the adjacent retaining walls. In clear contrast to this, the portals at the exit areas of the tunnel are made of precast concrete elements. A structural separation of the differently designed entrance and exit areas is formed by ventilation partitions made of acrylic glass. These walls serve to separate the fresh and exhaust air between the two tubes.

2. Building design

2.1 General

The new tunnel consists of two separate tubes, each with three lanes. It has a length of 3,074 m (north tube) and 3,070 m (south tube). The maximum overburden is approx. 134 m. At the west portal, the center distance of the two separate tubes is approx. 26.5 m. It 138 New construction Tunnel Jagdberg near Jena(A 4) increases to approx. 35.5 m, leaving a rock pillar of approx. 11 m to 20 m between the tubes. In each tube, there are three 3.50 m wide traffic lanes and l m wide emergency walkways on both sides. There is an operations building in each of the two portal areas. The tunnel is approved for the transport of hazardous materials.

2.2 Geology

During the site investigations, it was determined that the tunnel crosses several geological layers and fault zones. While the higher-lying western part of the tunnel is predominantly in the Muschelkalk, the eastward sloping part, separated by a fault zone, is in the Röt. Fault zones were also encountered in the portal areas. In evaluation of the geological situation, the tunnel could be planned as a vault with open invert for approx. 80% of its length. In the portal areas and in the area of the Leutra fault, the arrangement of an invert vault became necessary.

2.3 Construction

The standard cross-section of the double-shell tunnel was designed as a clearance gauge RQ 33t with a clear width of 13.0m. The tunnel was built using the shotcrete construction method with a shotcrete outer shell and a reinforced concrete inner shell. The standard block length of the inner shell is 10m. This results in 306 blocks in the north tunnel and 294 blocks in the south tunnel. In the area of the entrances and exits, the block joints are designed as space joints and in the central part of the tunnel as compression joints. Invert and vault blocks were made separately by an unreinforced construction joint. Depending on the geotechnical conditions, the inner lining was constructed with a closed invert or with benchings. The standard thicknesses of the inner shell range from 40 cm to 60 cm, with differences between the cross-sections with open and closed invert. The invert and the arch are made of concrete of strength class C35/45.

Due to the geological-hydrological conditions, a drained tunnel with "umbrella sealing" was designed. The waterproofing consists of a plastic sealing membrane between the tunnel outer and inner lining. A geotextile was installed on top of the shotcrete waterproofing support as a protective carpet pad and a 2 mm thick plastic waterproofing membrane with signal layer was installed on top of it. In the area of the invert arch, there is an additional 3 mm thick plastic sealing sheet as a protective layer between the protective concrete and the elm drainage.

2.4 Drainage

In the area of the tunnel route, there is a permanent lowering of the groundwater level. Via the umbrella seal and the two external elm drainage pipes, the mountain water is collected in a collector pipe in the tunnel floor and discharged with the tunnel slope into the receiving water. Seepage water entering in the invert area is fed via a drainage layer of filter gravel to the longitudinal tunnel drainage, which runs parallel to the upland water collection pipe as a piggyback pipe.

In the final state, a DN 225 mountain water drainage runs on both sides of the tunnel in the area of the hawser. At intervals of approx. 300 m, the drainage penetrates the tunnel inner shell in drainage shafts and ties into a DN 300 collection line. This pipe leads through the tunnel to the neutralization plant. The extinguishing and cleaning water accumulating in the tunnel structure and the drag water accumulating in the entry areas is collected via slotted board channels and fed to the longitudinal tunnel drainage system via baffle shafts at intervals of approx. 50 m. The water is then collected in a drainage pipe. Two pollutant basins made of DN 3000 prefabricated reinforced concrete elements were arranged in the eastern tunnel apron to collect the extinguishing water and other liquids in the event of an accident.

2.5 Exhaust air center

Due to the length of the Jagdberg Tunnel, a complex ventilation concept is required that minimizes the pollutant load at the portals and is also designed for a possible fire. A smoke extraction cross-passage located approximately in the center of the tunnel, in conjunction with a 140 m high exhaust shaft, divides each tube into two ventilation sections.

At the transition to the smoke extraction cross shaft, the block length had to be increased to 14.60 m. The intersecting blocks were designed to be smaller. The intersection blocks were designed with an inner formwork thickness of 70 cm and a closed bottom. The transition area from the main tubes to the smoke extraction cross pass and from the cross pass to the smoke extraction shaft is a special feature. Spatial intersections were implemented to optimize the flow. Instead of standard formwork carriages, conventional timber formwork was used for the construction. Self-compacting concrete was used for concreting the elms and ridges separately.

The inner diameter of the exhaust shaft is 6.70m. The shaft can be inspected and checked by means of a drive-in system. In addition, a single stile ladder with retractable rest platforms is installed. In the event of a fire, the gases are extracted from one half of the affected tunnel via the exhaust air shaft, thus preventing the entire tunnel from being filled with smoke. In normal operation, mechanical longitudinal ventilation by means of jet fans provides the necessary ventilation in the tunnel.

2.6 Technical equipment

The tunnel's operational equipment includes:

  • Lighting, ventilation,
  • fire alarm system,
  • video surveillance, loudspeakers,
  • Traffic control equipment,
  • emergency call stations, tunnel radio,
  • fire extinguishing equipment,
  • height controls,
  • Escape route marking,
  • guidance facilities.

To support firefighting by the fire department, the Jagdberg tunnel was equipped with an automatic fire extinguishing system (FAS) in the event of a fire. The FFFS is designed as a stationary foam extinguishing system. Approximately 20,0001 foam can be generated per minute by means of compressed air from the 4,0001 water available. The system is designed to prevent the spread of fire in the tunnel by containing the fire. The BBA distribution lines run in two parallel pipe runs under the tunnel ceiling. Rotors located at constant intervals along the distribution lines are used to discharge the extinguishing agent.

Each extinguishing area is equipped with 8 rotors. The FFFS is also activated automatically, if required, after the end of the self-rescue phase. Automatic fire detection is provided by a fire alarm cable on the tunnel ceiling. It registers both absolute temperatures and temperature rises.

Tunnel safety is a top priority in tunnel operation in Germany. Thanks to the installation of 10 cross passages, every second of which is passable for rescue vehicles, the maximum escape route length in the event of an emergency is only 300 meters. The cross passages are equipped with fire protection gates. Due to the tunnel length, five breakdown bays are provided in each of the two tubes. The width of the additional retaining strip arranged in the approx. 50 m long breakdown bays is 2.50 m. At each breakdown bay, the two tubes are connected by a passable cross-passage. Emergency call and fire extinguishing facilities are located at a distance of approx. 140 m. Along the emergency walkway, emergency fire luminaires with escape route markings are located on the side of the cross-passage at intervals of no more than 24 m. Both tubes are continuously monitored by video. An active guidance system was installed to further optimize the escape route marking.

3. Construction

3.1 Tunnel driving

Tunnel excavation began on September 25, 2008, with a ceremonial tunnel stop on the south tube. Tunnel breakthrough already took place on August 18, 2009 in the south tube and on September 3, 2009 in the north tube. Both tubes were driven simultaneously from the west and from the east. As it was not possible to transport earth masses from the eastern tunnel drive for traffic reasons, approx. 500,000 m3 of earth material had to be temporarily stored at the east portal first. The excavated masses from the western drive, on the other hand, could be transported directly to the western construction area and installed there.

Both tubes and the crosscuts were excavated using the closed construction method. Only in the portal areas was approx. 130 m (east) and approx. 10 m (west) excavated using the cut-and-cover method. The Jagdberg tunnel was excavated using the shotcrete construction method. In this method, the cavity is excavated in short sections by drilling and blasting and then immediately secured with shotcrete, reinforcement and anchors to prevent the rock from caving in. The tunnel tubes were excavated with cut-off lengths of 0.80 m to 2.0 m using the spherical driving method. For the bench and invert, the cut-off lengths varied between 1.60m and 3.0m. Due to the geological conditions encountered during driving, it was necessary to extend the invert in some areas.

3.2 Exhaust shaft

The exhaust shaft is located approximately in the middle of the tunnel between the two tunnel tubes. The raise-boring method (upward drilling) was used to construct the exhaust shaft. With the help of a pilot borehole (DN 146 mm) from the ground surface to the cross cut, the information on the geological structure of the rock in the actual location of the future shaft was specified. Once the pilot hole had been drilled, the drill pipe for the extension boring head could be inserted into this hole and the boring head attached to the base of the shaft. The extension drill head was pulled upwards in several stages, with the drilled material falling down into the crosscut and being conveyed from there. The borehole created in this way (diameter 1800 mm) was used as a chute hole during the subsequent development of the shaft shell in order to be able to carry out conventional driving and development of the shaft from above. The excavated material from the shaft was removed downwards and transported away from the cross-cut. After approx. 80 days, the sinking of the shaft with a maximum shell diameter of 8.10 m was completed. The shaft wall was secured and the construction tolerances compensated for using at least 30 cm of shotcrete. The inner shell with a thickness of 20 cm was then placed by means of sliding formwork and the planned inner diameter was produced. In the lower third of the shaft, which is located in the reddish area, a seal was installed between the outer and inner shells of the shaft. This seal serves to protect the inner shell from concrete-aggressive water from the Röt.

3.3 Tunnel lining

The final stage of the structural work was the installation of the concrete inner lining, which ensures the long-term stability of the structure. The production of a vault block was carried out in 24-hour cycles, with concreting taking 6-8 h, depending on the season, and curing taking approx. 10 -12 h until the minimum compressive strength of 3-5 N/mm2 was reached. For concrete curing, three curing carriages were available for each tube. Water wetting was realized by means of a cold fogging system with electronic monitoring. Monitoring of the climatic chambers was fully automatic with measuring sensors and data recorders.

3.4 Dewatering

During excavation, rock seepage was collected in the sections of the closed invert under the roadway and drained off via a DN 200 drainage pipe. After installation of the inner lining, this construction drainage was backfilled with cement. In the areas of the open invert, the water was collected in special pump sumps and fed to the receiving water course via collector pipes.

In the course of construction, wet spots were found in the areas of open bottom in the Röt. Since the rock water occurring in the Röt is generally aggressive to concrete, additional sealing measures were necessary. Four reinforced concrete barriers below the roadway prevent water from reaching the concrete foundations in this area. In addition, rock injections were made in a semicircle under the barrier structures. This allowed the water-bearing areas to be sealed off and the accumulating water to be fed to the barrier structures.

3.5 Fire tests

In May 2014, extensive fire tests were carried out in the Jagdberg tunnel. The tests were carried out with the aim of ensuring the fault-free functioning and effectiveness of the automatic fire detection system and the stationary FFFS. The fire load was applied by fire pans filled with gasoline or n-heptane and by the real fire of a passenger car (scrap vehicle). During the fire tests, the roadway was protected in the area of the fire by covering it with rock wool insulation and sheet steel panels. The technical installations inside the tunnel were also protected from flames and radiation effects by mineral insulation materials. All the tests carried out were successful. Automatic fire detection took place after 60 seconds and thus satisfied the requirements of RABT 2006. In the fire test with n-heptane, the FFFS was triggered manually when full fire was reached (20 seconds after ignition) and an extinguishing area was activated at the fire site. The fire was extinguished after 40 seconds. The real fire test with the passenger car ran in the automatic program. Automatic fire detection took place 7:40 min after ignition of the passenger car. With the automatic fire detection, the stationary FFFS were activated and the extinguishing lines were automatically filled within one minute. At the same time, the emergency fire lights on the tunnel walls and the escape route orientation lights at the edge of the roadway went into operation. After a system-set delay time of 3 min, the foam application began. As a result, the fire was contained within one minute to such an extent that only a residual extinguishing in the vehicle interior by the fire department was necessary. The effectiveness of the fire detection system and FFFS for all fire scenarios performed was successfully demonstrated.

3.6 Dismantling of the roadway

After the commissioning of the new section with the Jagdberg tunnel, the old route of the A4 was dismantled over a length of approx. 10 km including the Schorba/Milda junction.

The construction of the new Jagdberg Tunnel eliminated an extremely disruptive bottleneck on the A4. With the new alignment outside the ecologically sensitive Leutratal nature area and the dismantling of the old alignment, valuable habitats were returned to nature.

3.7 Traffic clearance

Traffic clearance for the tunnel and the route in the direction of Eisenach took place on October 30, 2014.On November 18, 2014, traffic could also be released on the Görlitz directional roadway.

4. Literature

DEGES Deutsche Einheit Fernstraßenplanungs- und -bau GmbH (Hrsg.): Verkehrsprojekt Deutsche Einheit Nr. 15, A4 Eisenach - Görlitz, Streckenabschnitt: AS Magdala - AS Jena/Göschwitz „Leutratal", Tunnel Jagdberg. August 2014 



  • Country: Germany
  • Region: Thuringia
  • Tunnel utilization: Traffic
  • Type of utilization: Road Tunnel
  • Client: Federal Republic of Germany, Land of Thuringia
  • Project Engineer: DEGES, Deutsche Einheit Fernstraßenplanungs-und -bau GmbH
  • Consulting Engineer: WBI Beratende Ingenieure für Grundbau u. Felsbau GmbH
  • Test engineer: Ing.-Büro Prof. Duddeck +Partner GmbH
  • Construction monitoring: Bung, Heidelberg/Müller+Hereth, Freilassing
  • Contractor: Baresel GmbH, Leinfelden-Echterdingen/Beton- und Monierbau GmbH, Innsbruck/Kirchhoff Leipzig Straßenbau GmbH & Co. KG
  • Main construction method: Trenchless
  • Type of excavation: Drill-and-blast
  • Lining: Shotcrete
  • No. of tubes: 2
  • Tunnel total length: 3,074.02 m (north bore), 3,070.65 m (south bore)
  • Cross-section: 125 to 155 m²
  • Contract Volume: 173 miil. Euro (roughwork)
  • Construction start/end: 2008-2013
  • Opening: November 2014