1.General

The Schwetzingen tunnel on the B 535 federal highway is part of the four-lane Schwetzingen-Plankstadt bypass. The B 535 was built from 1998 onwards to consolidate the federal road network in the Rhine valley near Heidelberg. It initially ran from Heidelberg-Kirchheim to Schwetzingen. With the construction of the Schwetzingen-Plank- Stadt bypass, the B 535 has now been extended in a westerly direction. In addition to improving traffic conditions for the Schwetzingen area, this also created an improved cross-connection between the A 5 and A 6 federal highways. Since the B 535 touches residential areas of the city of Schwetzingen in large areas, extensive noise protection measures were necessary to maintain the environmental quality. These noise protection measures include the construction of the Schwetzingen tunnel. The underground routing as well as adjacent noise protection embankments succeeded in minimizing the effects of the increased traffic volume for the residents.

2 Design of the structure

2.1 Geology and foundation

The Schwetzingen Tunnel is located in the area of the Neckar alluvial sand fan. During the site investigations, the typical ground stratification for the area was encountered: Beneath the topsoil are slightly sandy clays or sandy to gravelly silt, which is replaced by gravel and sand layers in medium-dense to dense bedding. For economic and hydrological reasons, it was decided that the route should run close to the surface. Since the groundwater level is below the foundation base, it was possible to dispense with a closed tunnel base and the tunnel was founded flat on strip footings. Over a length of approx. 360 m, soil replacement with a thickness of 0.3 m was required below the strip footings.

2.2 Location and cross-section

The Schwetzingen Tunnel consists of two tubes separated by direction of travel. The northern tube has a length of 650 m, the southern tube is 450 m long. The B 535 is widened to four lanes in the construction area. In accordance with the standard cross-section of the free section of RQ 26, the standard cross-section of RQ 26 t was selected for the tunnel. The carriageway width for each direction is 2 x 3.75 m, plus 1.00 m wide emergency walkways on both sides. The clear width is thus 9.50 m per tunnel tube. The minimum clear height between the road surface and the tunnel roof is 4.85 m and is made up of 4.50 m clear usable height and 35 cm usable structural space. At the start of construction, the road axis has a radius of R = 675 m, which changes into a straight line after a transition curve A = 300. The gradient from east to west is constant at 0.2%. In the transverse direction, a gradient of 2.5% is formed. The tunnel is designed as a rectangular cross-section with two tubes separated by a central wall. The tunnel walls are 1.00 m thick. The 90 cm thick tunnel roof runs parallel to the transverse slope of the carriageway. Walls and ceiling are made of concrete of strength class C 30/37 WU. Since the entire tunnel lies above the groundwater table and seepage water can drain off, the tunnel was not designed for water pressure. The tunnel was designed as a water-impermeable concrete structure in accordance with the Additional Technical Terms of Contract and Guidelines for Engineering Structures, Part 5 Tunnel Construction (ZTV-ING, Part 5). The waterproofing of the overfilled tunnel roof was carried out by means of a plastic waterproofing membrane covered by a 10 cm thick reinforced protective concrete. The tunnel was constructed in blocks with a standard length of 10 m, with shorter block lengths selected in the portal areas. The tunnel blocks are separated from each other by space joints, which are sealed with an internal elastomeric joint tape with a center hose and provided with a joint closure strip on the air side. The north tube of the tunnel has two emergency exits spaced approximately 240 m apart. While the first emergency exit, seen from the west, connects the two tunnel tubes, the second emergency exit leads directly to the outside. The arrangement of emergency stopping or breakdown bays was not necessary. The tunnel structure was integrated into the landscape in such a way that the natural terrain horizon was preserved as far as possible. Where terrain and embankment areas were newly created, they were designed by accompanying landscape management planning.

2.3 Tunnel equipment

The tunnel equipment was designed in accordance with the guidelines for the equipment and operation of road tunnels (RABT). The operations center is located in a single-story, ground-level operations building at the west portal next to the southern tunnel tube. Since the operations center is not permanently manned, all reports are received by the 24-hour police headquarters in Heidelberg. Fire alarms also reach the integrated control center in Ladenburg.

Power supply

Power is supplied via the nearest substation from the public medium-voltage grid (20 kV). A UPS system housed in the operations building ensures an uninterruptible emergency power supply for a period of up to 60 minutes.

Lighting

To illuminate the tunnel, a strip of high-pressure sodium lamps is installed in each tube. The adaptation lighting is designed as counter-beam lighting, the passage lighting as symmetrical lighting.

Ventilation

No artificial ventilation system is required for normal operation. Since the tunnel tubes are operated in directional traffic, the exhaust air flows out at the respective exit portal. In the event of a fire, a total of 6 jet fans are arranged in two approx. 23 m long fan niches in the tunnel ceiling in the north tube for longitudinal ventilation. No fans are required for the south tube due to its shorter length (< 600 m).

Traffic engineering

The tunnel is provided with basic traffic engineering equipment in accordance with the RABT, which includes portal barriers, height control and an upstream traffic control system. A median crossing is located in front of each portal.

Safety equipment

There are 6 emergency call stations in the tunnel and 4 emergency call pillars in front of the tunnel portals. In addition to self-luminous marking elements on the emergency walkways, escape route lighting facilitates orientation. The tunnel is video-monitored by 25 cameras. It is also equipped with a tunnel radio system and a loudspeaker system with 22 boundary horns.

Fire alarm systems

Line fire alarm cables are installed in both tunnel tubes. Manual call points and two manual fire extinguishers are provided in each of the emergency stations.

Drainage systems

The drainage of the traffic areas is carried out via slot channels, which are connected in sections to the longitudinal tunnel drainage system with a nominal diameter of DN 500. Manholes are located at the discharge points. At each discharge point, the slotted channels are equipped with a bulkhead with siphoning to prevent the spread of contaminated or flammable liquids in the event of an accident. An underground catch basin is provided adjacent to the operations building at the west portal. It is connected to the sewer system by means of a lifting device and an adjoining pressure line.

Extinguishing water supply

Both tunnel tubes are equipped with an extinguishing water pipeline, which is laid frost-free as a DN 150 wet pipeline underneath the roadway. The tapping points are located opposite the emergency stations in separate niches in the center wall.

Noise protection

On the first 30 m from the portals, the tunnel interior surfaces were provided with a highly sound-absorbing, rear-ventilated cladding in the form of aluminum cassettes. In the area of the one-sided tunnel tube, the free tunnel wall was additionally clad with highly absorbent cladding. The noise protection cladding has a total thickness of 10 cm and is flush with the adjacent unclad tunnel wall.

3. Construction

Construction of the tunnel began on March 31, 2008. Due to the low overburden of 0.5 to 2.0 m on average, the tunnel was built using the cut-and-cover method along its entire length. The excavation pits could be constructed with a slope inclination of 45°. Only on a length of approx. 50 m was shoring in the form of a tangential bored pile wall necessary due to nearby buildings - the distance between the tunnel outer wall and the edge of the house was only 3.50 m here. The individual blocks were concreted using the pilger-step method. In the area of the radii, the blocks were constructed with polygonal formwork. For the construction of the tunnel walls, a multiple-use formwork was used. The slab was concreted using a formwork carriage. Following the structural work, the tunnel was equipped for operation and the Schwetzingen tunnel was opened to traffic in December 2010.

 

 

• Region: Schwetzingen-Plankstadt, B535, Baden-Württemberg 
• Tunnel use: Road 
• Client: Fed. state/Land Baden-Württemberg on behalf of Regierungspräsidium Karlsruhe 
• Planner: RP Karlsruhe, Ref. 43 Civil Engineering 
• Contractor: Leonhard Weiss GmbH& Co.KG Bauunternehmung  
• Construction method(s): open cut (w/s)
• Tunnel length: 650m (northbound tube), 450m (southbound tube)
• Costs: 16.5 million € (construction works)/ 4 million € (operating technology)  
• Construction time: 04/2008 to 12/2010
• Start of operation: 12/2010