1. General

1.1 Task definition

In the course of the extension of the B 20 between Cham and the border to the Czech Republic, the construction of a bypass in the area of Furth im Wald became necessary due to a considerable increase of through traffic. According to the forecast for the year 2020, a traffic load of 14,000 motor vehicles/24 h is expected here. The 4.3 km long bypass starts at the existing Furth im Wald-Ponnholz junction coming from Cham with the construction of the 275 m long viaduct over the Chambtal. The route then runs under the Deschlberg in a tunnel built by mining. In the area of the Furth im Wald-Mitte junction, the connection of the new state road cross span to the bypass is built. Continuing north, the new state highway crosses the "Eschlkamer Straße" and the Chamb River in a covered low-level tunnel. Subsequently, the route runs in the Chambtalaue in a slight embankment position before it rises towards the railroad line and crosses it in a deep cut. At the northern end of construction, the Furth im Wald-Nord junction links the bypass with Vollmauer Strasse and Böhmer Strasse. The Deschlberg tunnel is the key structure of the Furth im Wald bypass. It was designed as a single-tube road tunnel with two lanes and a parallel rescue gallery. Two accessible cross passages were arranged to connect the main tube with the rescue stations. The location for the operations center was determined at the east portal.

2. Design of the structure

2.1 Geology and foundation

The geological conditions along the tunnel route are characterized by a monotonous sequence of light-colored schistose gneisses. The rock behavior during excavation was classified in the core area as predominantly stable to post-fracture. Due to the low permeability of the gneiss layers in the area of the tunnel level, it was assumed that most of the percolating precipitation water would run off along the compact gneiss layer at the Deschlberg. The Deschlberg tunnel lies below the mountain water table over large areas. Since no invert closure is necessary for structural reasons and the predicted water ingress is very low, the tunnel and the rescue gallery were designed as a drained tunnel with sealing by means of a plastic sealing sheet. Due to the good foundation properties of the in-situ soil, the tunnel floor and the embankments were founded shallowly.

2.2 Location and cross-section

With a total length of 745 m, the tunnel crosses the Deschlberg north of Grasmannsdorf. The maximum overburden in the overlying gneiss replacement rock is about 45m. The construction area itself is neither crossed nor tangent to public traffic routes. The RQ 10.5T was selected as the standard cross-section for the main tube in accordance with the RABT. The carriageway width is 7.50 m plus the 1.0 m wide emergency walkways on both sides. The 2-lane main tunnel is connected to the parallel, accessible rescue tunnel with a clearance of 2.25 x 2.25 m via two cross passages located at the third points. The alignment of the main tube in plan runs at the west portal in a left-hand curve with R=700 m and then merges with a clothoid with A=300 m into a straight line. 79 m before the end of the tunnel another clothoid with A=250 m starts and leads to the east portal. The gradient from the west portal to the high point lies in the rounding of the crest and rises on average by 0.20%. From the end of the rounding after 199 m from the west portal to the end of the tunnel, the gradient runs with a constant gradient of 1.0%.

2.3 Structural design

The static system consists of a flexurally rigid system with section joints in the longitudinal direction, and as a flexurally rigid frame in the transverse direction. Rescue stations are located at the two portals, and the service building with the extinguishing water basin and a pollutant basin is located at the east portal.

Drainage systems

Drainage under the carriageway in the area of the traffic lane in the direction of Cham is provided by longitudinal pipes with a diameter of 300 mm of construction material class A. These are laid on concrete supports. These are laid on concrete supports. Inspection chambers are located at intervals of 50 m, the chamber cover corresponds to class D400, is watertight and can be locked. At the northern edge of the carriageway towards Cham, the drainage channel was installed as a slotted channel with a diameter of 300 mm. As special components, a baffle shaft and a cleaning channel were added at intervals of 50 m. The DN 200 cast iron drainage system is installed in inspection chambers. Drainage in the transom area on both sides of the tunnel tube between the outer and inner shells is provided by an elm drainage pipe of the rock drainage system with a pipe diameter of 200 mm. The drainage pipe is laid in filter concrete 16/32. Cleaning shafts are located in niches at intervals of 70 m. The shaft cover complies with class B125, is daywater-tight, lockable, hinged,- oil- and petrol-resistant. In the area of the open invert parallel to the collector pipe of the drainage system, the drainage is carried out via a bottom drain of the rock drainage system with a pipe diameter of 200 mm.

2.4 Tunnel equipment

In order to ensure safe traffic routing, avoid critical incidents, protect tunnel users and support emergency services in the event of a disaster, the tunnel was equipped with the following equipment in accordance with the RABT:

Tunnel Central Facilities / Energy Supply

The east operations building is integrated into the forebay of the east portal. The extinguishing water basin and the pressure boosting system for the extinguishing water supply are attached to the operations building. A UPS system housed in the operations building supplies all the safety systems of the tunnel and the operations building. The total electrical power is 400 KVA, the backup power supply with 100 KVA is provided by a battery system.

Tunnel lighting

The lighting in the area of the west and east portals is provided by a counter-beam lighting system.

Tunnel ventilation

The tunnel is ventilated naturally during normal operation, and in the event of a fire by means of semi-cross ventilation through the rescue gallery and the two cross passages. To maintain the air quality and for fire ventilation in the tunnel, 6 jet fans are installed as axial fans. For fire ventilation in the rescue gallery, four jet fans are mounted near the portal. They are used for longitudinal ventilation of the tunnel.

Tunnel safety

For tunnel safety, five emergency call stations have been arranged at 140 m intervals, five hydrants at 140 m intervals, two cross tunnels at 250 m intervals and five fire extinguishing stations at 140 m intervals. In addition, there is an automatic fire alarm system, video surveillance, radio and public address system. Two DN 150 extinguishing water pipes are located under the roadway in front of the embankments. Active guidance devices have been installed for escape route marking. The escape route is marked with LED lights at 20 m intervals.

Traffic engineering

The tunnel is equipped with basic traffic technology according to RABT. The traffic control equipment consists of traffic signals, yellow flashers, variable message signs, variable direction signs, half barriers, height trolls in front of the tunnel and double induction loops, emergency and electronic, an emergency call system and escape route markings. The 24-hour monitoring is carried out either via the traffic control center in Munich-Freimann or in Nuremberg-Fischbach.

3. Construction

Construction of the Furth im Wald bypass began with the groundbreaking ceremony on October 30, 2007. Construction work on the tunnel itself started on December 9, 2009 with the tunnel stop. The tunnel was built using the shotcrete construction method. First, the cavity was excavated by blasting and temporarily secured with a combined system of shotcrete, anchors and steel arches, depending on the rock conditions encountered. The waterproofing system was then applied and the in-situ concrete inner lining constructed. The excavation of the main tunnel was carried out as a partial excavation. First, the upper section of the tunnel cross-section, the calotte, was excavated, followed by the bench and invert. The rescue section was excavated in full. Approximately 100,000 m3 of rock was excavated from the tunnel and reused for road construction.

With the completion of the Deschlberg Tunnel, the first construction section from the Furth im Wald-Süd junction to the Furth im Wald-Mitte junction was opened to traffic on March 19, 2012. The overall measure was completed in September 2013.

• Region: Fürth, Freistaat Bayern
• Tunnel use: Road
• Client: Freistaat Bayern repr. by Staatliches Bauamt Regensburg
• Consultants: Staatliches Bauamt Regensburg; Müller-Hereth, Freilassing, iC-Consulenten, Salzburg
• Contractors: Jäger Bau GmbH, Schruns
• Total length: 745 m (Haupttunnel), 739 m (Rettungsstollen)
• Clearance profile: RQ 10,5T
• Contract value: 25,7 Mio. Euro (Rohbau), 5 Mio. € (BTA)
• Construction time: 12/2009 bis 03/2012