1. Task definition

As one of the most important west-east traffic axes in the European long-distance road network, the A 4 federal freeway connects the industrial locations in the Rhine/Ruhr and Rhine/Main conurbations with Thuringia, Saxony and the industrial centers of southern Poland.

Due to the importance of the A 4 as a transit route and its classification as European Road E 40, the expansion and new construction of the A 4, Eisenach-Görlitz, in connection with the new construction of the A 44, Kassel- Eisenach, was included in the catalog of the 17 German Unity Transport Projects and as "Priority Need" in the 1992 Federal Transport Infrastructure Plan.

Planning and construction of the A 4 date back to the 1930s, but the project between Dresden and Görlitz was never completed. When construction work was stopped in 1940, Weißenberg had just been reached. With the closing of the gap between Weißenberg and Görlitz, which had existed for almost 60 years, and the completion of the A 4 as a major European highway, the "Königshainer Berge" were also touched.

Under the decisive aspect of preserving the natural habitat, it was decided to plan a tunnel structure to pass under the area of the "Königshainer Berge" landscape conservation area.

At 3.3 km, this is currently the longest highway tunnel in Germany. It was planned in the interest of routing the highway in a way that is as environmentally friendly and compatible with the landscape as possible and demonstrates in an exemplary manner the high priority that is given to ecological aspects in modern road construction in Germany.

The planning provided for two tunnel tubes, each with a length of 3,290 m, operated in the direction of traffic. The clearance gauge is defined by the road cross-section RQ 26 according to the Guidelines for the Design of Roads, Part: Cross-sections (RAS-Q), which is reduced to cross-section 261 in the tunnel area. The two lanes of a tunnel tube each have a width of 3.50 m with 0.25 m wide shoulder strips on both sides and 1.00 m wide emergency walkways. This results in a total width of the clearance area of 9.50 m.

Both tubes rise from the west and east portals with a gradient of 0.50% towards the center of the tunnel. The radius of curvature of the crest is 70.000 m.

A distance of approx. 30 m is maintained between the roadway axes in the tunnel area, while this distance is reduced to a minimum of 20 m in the portal areas.

According to the guidelines for the equipment and operation of road tunnels (RABT), 4 breakdown bays with a length of approx. 40 m and a width of 2.50 m have been provided for each tunnel tube. The tunnel cross-section is also designed in these special areas so that the prescribed clear space is available above the bays.

Between the northern and southern tunnel tubes, 9 connecting tunnels have been provided as escape routes or for the passage of cars, ambulances and fire departments.

2. Structural design

2.1 Geological conditions

The geological and hydrogeological boundary conditions for the design of the structure are described in an expert report. The basis of this report was a detailed site survey with geological mapping. In addition, geophysical methods such as seismics and geoelectrics were used to localize the solid and loose rock areas. Above all, a total of 31 boreholes drilled provided important information on the geological situation.

The project area is located between Upper Lausitz and the Lausitzer Bergland in the Lausitz granite region. The tunnel runs in the so-called "Königshainer Granite", named after the eponymous type locality of the Königshainer Mountains.

This granite intruded the older Precambrian rocks during the Variscan mountain building phase. The overlying overburden was eroded over millions of years, so that the Königshain granite was exposed on the surface for the first time towards the end of the Cretaceous. For more than 60 million years it has been exposed to the changing climatic conditions and thus to the attack of weathering.

The solid rock, which was partly opened up in quarries and drilled, is primarily of two varieties, a light and a dark modification of the above mentioned Königshain granite. The light variety corresponds to a medium to coarse-grained granite of relatively uniform grain size. Its appearance is mainly determined by the light main aggregate components quartz and feldspar.

The dark variety differs from the light one by its porphyritic structure. While the light granite occurs almost throughout the project area, the dark granite is found only in the area of the east portal.

The unconsolidated rocks occurring at the surface can generally be divided into flowing clays and recent soil formations. In addition, the products of granite weathering in the uppermost meters of the weathering cover have unconsolidated character. The tile loams occur only in the area of the eastern portal and are maximum 3 m thick.

With regard to the interface structure, influences of a fault line located about 400 m to the south and extending from west to east on the area of the tunnel could not be excluded.

The great difficulties encountered in sinking borehole 10 had to be interpreted as a possible indication of a fault zone intersecting the tunnel axis.

The Königshain granite is today deeply weathered, many tens of meters, in part probably even to depths of more than 100 meters.

The weathering has extended into the depths along the steeply standing fissures and has disintegrated the formerly "healthy" granite into fissure bodies ranging from a few centimeters in diameter to several cubic meters in volume. In boreholes penetrating the tunnel route, very strongly weathered rock sections with loose rock character were drilled even at a depth of 50 meters.

Particularly in the village valley areas, there are very strongly weathered rock sections down to depths of at least 15 to 20 meters.

From a hydrogeological point of view, the permeability of the rock is significantly lower than in the "healthy" fractured rock, which shows a high permeability, because of the partly strong weathering of the granite. The natural mountain water table essentially follows the top of the terrain at a depth of 5 to 10 meters. In areas of higher permeability, it can drop to 20 m below ground level.

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 with a flattened crown compared to a circular vault.

Two types of construction were used in the invert area. In good rock conditions, the core area of the tunnel was given an open invert.

In the entrance areas, in the area of geological faults and severe weathering, a shallow invert vault was used. The total excavation area was approx. 80.50 m2 for the standard cross-section with open invert, and approx. 93.80 m2 for the standard cross-section with flat invert vault.

The total excavation area of the breakdown bay with open invert was 103.50 m2, with flat invert arch approx. 128.00m2.

The tunnel design was based on a double-shell construction method:

After excavation of the tunnel and placement of the outer shell of shotcrete, the waterproofing was laid and the in-situ concrete inner shell was installed.

As a rule, the in-situ concrete shell of B 25 had a wall thickness of 30 cm and is unreinforced. Only in the portal areas and in the fault zones was a 40 cm thick reinforced inner lining required.

In the area of the breakdown bays in good geological conditions, a 40 cm thick reinforced inner lining was also required, while the breakdown bays in poor geological conditions were given an invert arch and a 60 cm thick reinforced inner lining.

Designing and dimensioning the tunnel tubes to withstand the entire mountain water pressure of almost 40 m was not recommended for technical and economic reasons. The rock was therefore drained along the entire length of the tunnel, thus almost completely relieving the water pressure in the tunnel surroundings.

In these NW 200 mountain water drainage pipes, the water seeping in from the rock is collected on both sides of the tunnel tubes and conveyed in the direction of the portals. At intervals of 50 m, niches with a control and cleaning shaft are arranged in the tunnel wall, through which the pipes can be flushed. From these shafts, the mountain water is discharged via short-closed NW 200 cross pipes to the mountain water collection pipe, which is connected to the roadway drainage system outside the portals.

Roadway drainage is provided by slotted channels at the low point of the roadway, which is connected to the longitudinal drainage line via syphoned cross pipes. The longitudinal drainage line is connected to underground reservoirs that are drained as needed.

Due to the presence of mountain water, the tunnel was sealed in the vault area along the entire length of the tunnel. This sealing consists of a 2 mm thick foil (without signal layer), which was laid on a protective fleece with a weight of 500 g/m2 and the fastening discs fixed to the shotcrete.

The joints of the sheeting, welded with hot air, were provided with a double seam to allow leak testing with compressed air.

2.3 Operating facilities, equipment

The safety concept for the tunnel envisaged connecting the north and south tubes via 9 transverse tunnels. This also provided for the possible passage of motor vehicles.

Each tunnel tube was provided with four breakdown bays, which are located in the entrance area of the escape tunnels and have a length of 40 m with a cross-section widening of approx. 2.50 m on one side.

Operations control centers are assigned to the two portals, which were covered over in their final state. Thus, the scale hardly comes into its own.

The tunnel is equipped with lighting, ventilation and the usual safety devices.

The lighting system installed is adaptive lighting and passageway lighting with high-pressure sodium lamps using counter-beam technology. It is controlled by measuring units in front of the portals and comparative interior measurements.

Due to the tunnel length, a ventilation system is required for both tunnel tubes, which are used exclusively for directional traffic. Longitudinal ventilation with jet fans proved to be the optimum solution. In order to cope with all traffic situations and also in case of fire, 24 jet fans were installed per tunnel tube. In case of fire, revision circuits were made.

The jet fans were installed in pairs in the free tunnel cross-section above the traffic area. There are 6 pairs of fans in each of the portal zones, spaced 100 m apart.

The fans are controlled by CO and visual opacity monitors installed in the tunnel tube. With vehicle traffic flowing at average speeds of V = 80 km/h, each tunnel tube ventilates itself.

Emergency call niches in accordance with RABT have been installed at a distance of approx. 165 m from each other. Signs point out the emergency niches and the cross tunnels as escape routes.

Fire line detectors have been installed at intervals of approx. 150 m. Furthermore, transmitting and receiving antennas for BOS radio, a radio transmitter for traffic announcements, a television monitoring system and announcement facilities were installed at the emergency call niches.

Since the tunnel is operated fully automatically when unmanned, a control system was required in conjunction with a remote control system to the nearest highway maintenance facility.

A traffic control system was arranged upstream of the tunnel tubes to slow down or stop traffic in the event of technical faults or accidents.

2.4 Construction method

With the exception of the portal closure walls and the operating building in front of the portal closure wall, the tunnel was built using the closed construction method.

In view of the prevailing rock conditions, the tunnel tubes were excavated using the shotcrete construction method, since this method is technically and economically best suited to the expected highly variable conditions. The suitability of the safety measures implemented in each case and of the temporary lining with shotcrete, steel arches and anchors was checked by accompanying deformation measurements and by special measuring cross-sections.

The tunnel was excavated in the hard rock area by blasting. In the entrance sections with possible loose rock areas, the use of a tunnel excavator or a hydraulic chisel also had to be provided for.

For the excavation and support work, a project-related excavation classification with different excavation classes and assigned support types for the heading classification was developed on the basis of the preliminary geotechnical investigation, taking into account the excavation cross-section and the planned construction method.

Rock behavior, excavation and support system were combined and defined by profile types. The excavation cross-section is therefore basically divided into calotte, bench and floor, which are excavated one after the other.

The height of the calotte excavation was determined by the dimensions of economically operating equipment.

The height of the hawser excavation was determined by the calotte bottom and the residual excavation of the invert, which usually preceded the concreting of the invert arch and the benches by only a short distance. This avoided damaging softening or loosening of the rock in the invert area. The hawser excavation followed the calotte excavation at a distance of about 100 - 200 m. However, since the blasting scheme in the bench is simpler than that in the calotte, and in addition the advance speed is much higher, the bench excavation did not follow continuously, but at intervals. In difficult conditions, for example when the rock deformations became too great, the distance between the calotte and the hawser was determined by geotechnical specifications and limited to the tolerable extent.

The portal areas, including the service buildings, were constructed using the open cut method. The transition to the open forebay is formed by a portal end wall clad with natural stone. For ventilation reasons, a partition wall (embankment fill with wall attachment and 7.50 m total height) was required between the two tunnel tubes over a length of approx. 30 m in front of the portals.

3. Construction execution

The construction contract was awarded on the basis of the tendered design. No special proposals were used. Prior to the start of construction work, it was decided that the 220 m long western tunnel section, which was planned using the cut-and-cover method, would also be built using the mining method.

Construction officially began with the tunnel cut on March 27, 1996, at the east portal. The preliminary cuts in the east and west, including the tunnel stop walls, were excavated in their final state, so that no measures for slope stabilization were necessary. In accordance with the ground conditions and the tunnel cross-section, the cavities were then driven into the rock at four excavation points from all portals using the mining method.

The excavation of the entire cross-section was carried out in three partial excavations - calotte, bench and invert - spatially and temporally divided using the drill-blast method. The total excavation volume consisted of about 500,000 m3 of rock. The tunnel received a double-shell lining, an outer shell as safety shoring and an inner shell as concrete lining.

With the excavation proceeding in sections and the rock masses being removed, the rock had first to be secured. For this purpose, the outer lining of B 25-grade shotcrete was used. In good rock conditions, steel fiber shotcrete was used to reinforce the shotcrete shell, otherwise mesh reinforcement was used. In a second subsequent work step, the inner shell of cast-in-place concrete was then installed after the installation of a 2 mm PE foil waterproofing layer. A formwork carriage was used, which could be used continuously with each concreting section. The concrete was placed in block lengths of 10m. During tunnel driving, the construction of the breakdown bays and connecting tunnels was also carried out in the same way. For the curing of the freshly concreted inner vault, a chambered curing car was used, the geometry of which was adapted to the shape of the vault and which ensured uniform moistening of the concrete by means of appropriate steam and spraying equipment.

This was followed by work in the area of the portals, with the portals themselves being constructed in an inclined form from B 35 reinforced concrete using the open-cast method. At the east and west portals, a partition wall was installed between the carriageways. A noise barrier had to be built above the east portal to separate a path crossing directly behind this portal.

For the construction of the two service buildings including ancillary facilities, it was also necessary to build retaining walls up to 3.00 m high, which were constructed as dry stone walls from typical local granite.

The work was completed with the road construction and drainage work as well as the installation of the tunnel equipment and operating facilities, so that the work on the tunnel was also completed when the new section of the A4 freeway was opened to traffic on March 8, 1999.

4. Literature

[1] Bundesministerium für Verkehr, Bau- und Wohnungswesen: DEGES, Deutsche Einheit Fernstraßenplanungs- und bau GmbH: Dokumentation aus Anlaß der Verkehrsfreigäbe am 8. März 1999

[2] DEGES, Deutsche Einheit Fernstraßenplanungs- und bau GmbH: Baubeschreibung

[3] DEGES, Deutsche Einheit Fernstraßenplanungs- und bau GmbhH: Erläuterungsbericht zum Bauwerksentwurf

 

 

• Country: Germany
• Region: Sachsen
• Tunnel utilization: Traffic
• Type of utilization: Road tunnel
• Client: Bundesrepublik Deutschland und Freistaat Sachsen
• Consulting Engineer: Müller+Hereth lng.-Büro für Tunnel- und Felsbau
• Contractor: Hochtief AG, Universale-Bau GmbH, Schachtbau Nordhausen
• Main construction method: Trenchless
• Type of excavation: Drill-and-blast
• Lining: In-situ concrete
• No. of tubes: 2
• Tunnel total length: 2 tubes, each 3,300 m
• Cross-section: 80.5 – 120 m²
• Diameter: 10.65 m
• Contract Volume: approx. 137 mill. DM
• Construction start/end: 1966 till 1999
• Opening: March 1999