1. Task definition

The town of Hausach is located at one of the most important east-west crossings of the Black Forest, which starts at the Rhine valley highway near Offenburg and ends in the Villingen-Schwenningen area at the Stuttgart-Bodensee highway.

For decades, the citizens of Hausach had to endure the immense through traffic in the Kinzigtal on the federal highway 33 of up to 20,000 vehicles per day. After lengthy planning and approval procedures, construction of the Hausach bypass for the B 33 finally began in July 1990. The bypass has a total length of 4 km and 2.6 km of connecting sections with a total of 14 bridge structures. The centerpiece of the bypass is the 1085 m long Sommerberg tunnel. The original alignment of the B 33, defined in 1969 in accordance with §16 of the Federal Highway Act, included a tunnel structure only 450 m long. Numerous objectors demanded further noise protection and a better urban development adaptation of two residential areas affected by the new road, which ultimately led to a route shift to the north and thus to a longer tunnel structure.

2. Design

2.1 Geological and hydrogeological conditions

The route of the tunnel structure to be constructed by mining excavation passes through a diverse rock mass. Paragneiss and syenite are the most common rocks. The mostly dark, massive and medium-grained syenite rocks, which are dissected at wide tectonic divides, form the central section in the tunnel for about 320 meters. To the west and east of the aforementioned central section, paragneisses predominate. They are also mostly dark, but in contrast to the syenite, banded rocks. Amphibolites and calcareous silicates are occasionally intercalated in the schistosity. The tectonic contact between syenite and paragneiss occurs on both sides via fault zones up to 20 m thick.

A geological feature is present on the first 335 m from the west. There, a rock known as "Bröckelfels" is encountered, completely weathered but not redeposited.

A pegmatite dyke about 5 m thick in the friable rock with unusually large tourmaline suns should be mentioned as a mineralogical feature.

The maximum overburden of the tunnel ridges is encountered at about station 740 - 910 with approx. 73 m.

A closed groundwater table is not present in the entire tunnel area. However, numerous water ingresses are recorded from the fissure water level, which fluctuates depending on precipitation. The total discharge is 1.5 to 2.5 l/sec. While the friable rock in the west is completely dry, water inflows occur between stations 200 and 300 in a narrow area of intensely fissured paragneiss or syenite. The strongest water inflows are in the paragneisses of the eastern half of the tunnel and are mostly tied to the crosscutting and steep faults.

2.2 Design parameters

The standard cross-section of the 1085 m long tunnel corresponds to the 12 t road cross-section according to RABT. Approximately in the middle of the tunnel, there is a breakdown bay that is about 40 m long and 2.50 m wide on both sides. The excavation area of the standard cross section is approx. 82 m2 , that of the widening area approx. 144 m2 .

The tunnel alignment rises uniformly from west to east at a rate of 0.45% to the high point, which is still in the tunnel about 60 m before the east portal. The tunnel lies in a right-hand bend in its entire area, which, coming from the west, initially leads about 125 m into the tunnel with a radius of R = 900 m. This is followed by an approx. 245 m long bend. This is followed by an approx. 245 m long transition curve to the subsequent right-hand curve with R = 7,500 m. The tunnel is located in this curve. This radius is maintained until shortly before the eastern end of the tunnel. The one-sided transverse gradient is 3% in the west and decreases to 2.5% in the larger radius.

2.3 Arrangement of operating facilities

Two caverns with the same excavation area as the standard cross-section branch off at right angles to the roadway to the north from the breakdown bay located approximately in the center of the tunnel. The western cavern is used for electrical supply, the eastern one for tunnel ventilation. For a 1 km long tunnel with two-way traffic, the following ventilation systems can be considered:

•  Continuous longitudinal ventilation
•  Longitudinal ventilation with central exhaust shaft
•  Reversible semi-transverse ventilation.

The high proportion of heavy truck traffic and its almost uniform directional distribution on average cause the tunnel air column to constantly oscillate, which results in constant ventilation of the portal sections over a length of 100 - 300 m. The tunnel air column is then continuously circulated through the tunnel. However, in the middle section there is a zone where the tunnel air is relatively rarely replaced. This circumstance, as well as calculations of operating costs and assessment of immission friendliness proved a central exhaust system to be the most favorable solution. The ventilation and electrical caverns are connected at their northern end by a cross passage. From the ventilation cavern, an approximately 19m long gallery with an excavation cross-section of about 34 m2 leads to the base of an exhaust shaft running vertically upward, which is about 73m deep and has an egg-shaped cross-section with dimensions of about 6.50 x 8.50m. This cross-section also houses a forced ventilation pipe for the cavern.

The operations building is located immediately adjacent to the west portal on its south side. An additional electrical room is provided as a single building about 20 m behind the east portal.

2.4 Construction method and excavation concept

The entire length of the tunnel was excavated using the "New Austrian Tunneling Method" (NOT). Following the excavation, a shotcrete lining was installed as initial support, which was reinforced with tunnel arches and reinforcing steel meshes, and if necessary also with anchors.

In the invitation to tender, driving in the opposite direction was planned. From the west, the rock in the area of the friable rock was mechanically loosened for about 250 m of tunnel length. The blasting required in the syenite and paragneiss, on the other hand, was carried out from the east. Whereas in the west drive, following the calotte at a short distance, the bench and the floor were excavated immediately, from the east only the calotte was driven up to the breakthrough with the west drive. After the breakthrough, the excavation of the bench and the floor was carried out in reverse from west to east, whereby the excavated material could be driven off over the still existing floor of the calotte heading in the direction of the east. Most of the excavated material could be used for the B33 road construction project.

2.5 Sealing and drainage

The tunnel has a waterproofing system between the outer and inner shells to keep out mountain water. A 500 g/m2 staple fiber fleece is used, which was installed after spraying a sealing carrier onto the treated surface of the shotcrete lining. This was followed by a film of PE plastic sheeting (d = 3 mm). At the foot of the elm trees, a permanently effective bilateral mountain water drainage system consisting of a DN 150 filter pipe laid in single-grain concrete is arranged, at which the sealing sheeting ends.

Both the drainage and the tunnel carriageway are drained to the west. The carriageway is drained via a hollow shelf channel connected to a collector pipe leading to the west. After passing a light liquid separator, the roadway drainage is fed to the sewer system and from there to the sewage treatment plant, while the mountain water is discharged directly into the Kinzig River.

2.6 Interior design

Depending on the rock conditions encountered, the reinforced concrete inner lining will be installed with or without a bottom arch. The thickness of the inner lining varies according to the different geotechnical conditions. In two working steps, the embankments and the invert, respectively, were constructed. The formwork carriage then ran on these components. The tunnel cross-section was designed in such a way that a formwork carriage suitable for the normal cross-section and divisible in the middle could be used for the widened cross-sections in the breakdown bays or in the portal areas to be equipped with noise protection. The maximum length of the concreting sections was 11m. Along the block joints, an external joint strip was welded radially around the sealing sheet and concreted in with the inner lining.

The gap in the ridge between the shotcrete outer and inner shells was closed with a secondary grouting operation that followed the concreting operation.

The tunnel portals, which are cut quite shallowly at approx. 30° in line with the existing terrain, have a collar whose reveal area increases in the ascending direction from approx. 0.70 m to 1.60 m and which is inclined outward at its apex by 20° from the perpendicular. The collar is structured by collar strips of 3 x 6 cm inserted parallel to the apex slope.

2.7 Pavement structure

The pavement structure is constant over the entire tunnel area. It consists of 4 cm surface course, 8 cm binder course, 14 cm bituminous base course and 34 cm frost blanket. Base course and 34 cm frost blanket. In the area of the cross-sections with invert vaults, the area between the top of the invert and the bottom of the frost protection layer is filled with a gravel base course. Emergency walkways, each 1 m wide, are arranged on both sides of the carriageway, under which cable duct shaped blocks with 8 or 9 empty pipes are accommodated. The extinguishing water pipe is located laterally next to the northern foundation in the roadway at frost depth.

2.8 Equipment and operating facilities

2.8.1 Lighting

The basic lighting system extends along the entire length of the tunnel and consists of a daytime stage and a night stage. The night stage also serves as safety lighting, which is powered by batteries in the event of a power failure. The adaptation lighting in the portal areas can be adjusted in six stages depending on the external brightness. The tunnel walls were brightly coated up to a height of 2 m.

2.8.2 Ventilation

Two infinitely variable axial fans with a drive power of 90 kW each are required for central extraction in the center of the tunnel. 8 jet fans mounted under the tunnel ceiling, each with a drive power of 22 kW, serve to equalize the pressure in the two halves of the tunnel. For tunnel air monitoring, 6 CO measuring points and 6 visual opacity measuring points are provided. For inspection work, an access system with permanently installed elevator rods and a mobile access unit with a fold-out platform is installed in the exhaust air shaft.

2.8.3 Fire protection

A temperature sensor cable is arranged along the entire length of the tunnel for rapid detection of a fire source. Hydrants and hand-held fire extinguishers, as well as hand-held fire detectors in the emergency call niches, complete the fire protection system.

2.8.4 Communication facilities

Emergency telephones are installed at 160 m intervals in the tunnel tube. A telecom line can be used to contact the nearest police station. The police can observe what is happening in the tunnel via a video system equipped with 14 cameras and address the tunnel users by radio. An emergency call pillar is located in front of each portal.

2.8.5 Electrical supply

The connection to the 20 kV network with two separate ring feeds is located in the operations building at the west portal together with the control and supply equipment for the adaptation of the west portal. The single building located at the east portal is used for the adaptation control at the east entrance.

The electrical cavern located next to the ventilation cavern houses the switchgear for the exhaust air systems.

The three stations communicate via a central control system, which also handles traffic control and signal management. The control room of this central control system is also located in the operations building at the west portal and allows the operator an overview of the operating status and traffic conditions at any time.

2.8.6 Noise protection

Noise protection measures have been provided where residential areas are exposed to direct or indirect noise immission. For this purpose, the area of the western tunnel portal was lined with sound-absorbing elements.

3. Construction

3.1 Pre-cuts

At the start of construction, a 130 m long pre-cut was made at the eastern portal via the access road from the B 294/eastern Kinzig bridge. This pre-cut was initially constructed at calotte level and later deepened with the elm bed excavation. As far as possible, the embankments were grassed in their final position.

Extensive earthworks and slope stabilization were required to create the pre-cuts at the west and east portals. The precuts were secured at the face in the area of the tunnel openings with shotcrete d = 10 cm. In the western area, the service building had to be integrated into the precut. The lateral slope inclination was 45° and was secured with sheeting and steel mesh, with the north-facing slopes being secured with a Delta Green wall. In the area of the calotte, a reinforcement ring was created and anchored back into the rock. Above the portal, it was secured with textile grids and the rainwater was drained away in a circumferential drainage channel. The final stabilization of the forebays was partly carried out with vegetated embankments.

3.2 Tunnel driving

After completion of the portal support, the stoping was carried out. Due to the size of the excavation cross-section, the Sommerberg Tunnel was excavated in two or three sections, as specified in the tender. First, the dome was excavated from both portals with a cross-section of 55 m2 . On the west side, 4 air arches were set up for the calotte advance and a load-bearing shell of 30 cm thickness was pre-piled with spiles or plates, which rested on a foundation strip. The approach on the east side was the same, but due to the incline of the portal slope, the air arch shell was longer here (8 air arches). The tunnel and portal blocks, which were constructed using the cut-and-cover method, were formed from the outside, with the inside formwork being provided by the formwork carriage. The portal collars were constructed in a separate operation. Calotte driving was carried out in accordance with the planned excavation classes. After reaching the breakthrough point, which as expected was at about 360 m from the west, the next deeper excavation was excavated by bench driving, with the tunnel being constructed with invert vaults only in the areas close to the portal. The bench driving began in sections in the western part of the tunnel, followed by driving in the eastern part. Whereas blasting was used throughout in the eastern section, excavation in the western section was carried out by excavator, in some cases with loosening blasting.

3.3 Sinking the air shaft

In preparation for the raise boring, a target borehole was drilled, enclosed by a foundation ring in the egg-shaped profile of the later shaft. With the raise boring, the shaft was widened and sunk with a shaft excavator in the entire profile, with the excavated material being chucked down through the raise boring and removed through the drifted access gallery. The support was provided in accordance with the classes advertised for the air shaft. The shaft was concreted using climbing formwork. The top of the shaft was constructed with threaded terrament cement.

3.4 Inner shell

In accordance with the tender, the inner lining was installed in two steps. First, the invert vault or the banquettes were constructed with the elm drainages. The formwork carriage for the vault ran on this invert or banquettes. A Sicea formwork carriage was used for the standard cross-section. For the area with the widening for the noise protection at the west portal, the same carriage could be used in accordance with the design without any modifications; it was merely "placed further" here. Due to the same standard cross-sections of the electrical gallery, ventilation gallery and traffic tunnel, the formwork carriage was rotated in the caverns during construction of the inner lining and the inner lining was installed there. For the breakdown bay, a formwork carriage specially designed for this profile was used. The maximum block length in the breakdown bay was 8.22 m, and 11 m in the standard cross-section. The end walls of the breakdown bay were concreted using the standard cross-section carriage and an extended end formwork. The inner shell for the access gallery as well as the connecting gallery was constructed using locally adapted timber formwork in conjunction with Peri precast formwork elements. Formwork designed by Peri was also used for the inner shell of the ventilation shaft. All niches were constructed with special timber formwork in the course of block concreting. After construction of the inner shell, or at a later date, the bottom drainage, the fire-fighting water pipe and the emergency walkways with the cable protection pipes and the necessary cable pull shafts were constructed, and the raised kerbs and slotted channels were laid.

4. Literature

[1] Straßenbauamt Offenburg: „Der neue Weg, Neubau der B 33 Umgehung Hausach"

 

• Region: Hausach, Baden-Würtemberg
• Tunnel use: Road
• Client: FRG, represented by RP Freiburg
• Consulting Engineers: RP Freiburg, Philipp, Schütz u. Partner, Schindler + Haerter AG, Bühringer & Co.
• Contractors: Alfred Kunz GmbH & Co., ABB Leitungsbau GmbH, Dürr GmbH, Stang Bau GmbH
• Tubes: 1
• Total length: 1.085 m
• Cross-Section: 45 m²
• Contract Value: 42 Mio. DM (Rohbau), 5,6 Mio DM (BTA)
• Construction Time: 07/1990 bis 12/1995 (66 month)