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Löwenherztunnel, B 10, bypass of Annweiler

1. Task definition

Due to the ever increasing traffic in the communities of Rinnthal, Sarnstall and Annweiler with about 17,000 motor vehicles/24 h with a truck share of 14 % and a forecast value of 25,000 motor vehicles/24 h with a truck share of 19 %, planning for a relocation of the through traffic from the localities began as early as the end of the sixties. However, the relatively densely populated villages in the Queichtal valley left no room for a new road, so that the road planners had to lay the route high above the villages "in the mountain".

Although this routing was highly demanding in terms of engineering and relatively costly, it was the only way to protect the residents from very high traffic emissions (noise/exhaust fumes) and at the same time to significantly improve traffic conditions on the connection between Landau and Pirmasens.

Due to the topography of the Palatinate Forest, the route of the new B 10 federal highway, which was optimized in the interest of the residents and the preservation of the local living and settlement area, required numerous engineering structures. Thus, in addition to 26 bridges, numerous retaining walls and noise barriers, 4 tunnel structures had to be built, which, with their adjoining galleries and retaining walls, had to ensure the selected routing of the route in and along the mountain. Of the total 9.3 km long Rinnthal - Annweiler bypass, 3.0 km, or almost one third of the road, is routed underground "in the mountain". In addition to the 304 m long Kostenfelstunnel and the longest tunnel built in Rhineland-Palatinate (Staufertunnel, L = 1038 m) and the 790 m long Barbarossatunnel, the 900 m long Löwenherz Tunnel, named in reference to the medieval history of Trifels Castle, was to be built above Annweiler.

The aim was not only to build a tunnel structure that would be safe for traffic and durable, but also to preserve the landscape of the "Palatinate Forest Nature Park" and, at the same time, to lend acceptance and elegance to the unavoidable intervention in the natural landscape by means of a special design.

The topography and slope geometry in the area of the Annweiler bypass were decisive for the planning of the Lionheart Tunnel. Thus, in addition to the actual tunnel, an approximately 500 m long gallery and a total of approximately 140 m long retaining walls with heights of over 10 m were required.

Originally planned retaining walls adjacent to the tunnel portals could not be further pursued because of the poor subsoil conditions, which only permitted slope gradients of 1 : 1.75 and would have led to considerably longer and higher retaining walls, so that a gallery had to be planned in their place.

The ground plan geometry of the tunnel is determined by the alignment of the road with a constant alternation of circle and clothoid, the gradient first rises at 3.65% and then changes to a slope of 3.05%. The cross slope ranges from - 4.0 % to + 4.0 % depending on the fillet parameters.

In addition, ecological and microclimatic conditions determined the tunnel length. The shape of the tunnel cross-section had to be adapted to the functional (clearance gauge) and structural/technological requirements.

2. Structural design

2.1 Ground and groundwater conditions

The rock conditions in the area of the planned tunnel route were explored by drilling prior to the start of construction, which revealed that the tunnel crosses the "Oberrotliegende" over its entire length. The rock formation is characterized by relatively variable sedimentation, which can range from coarse-grained sandstones to fine-grained sandstones, siltstones and mudstones. The Upper Redstone is overlain by the "Lower Buntsandstein", which has a thickness of up to 80 m in the study area and shows a relatively uniform sedimentation. It consists mainly of fine-grained sandstones and siltstones.

The strata of the Rotliegend generally dip at an angle of max. 10° to the NW. The fracture couloirs are mostly steep between 70° and 90°. Main parting surfaces are both the fracture couloirs and the bedding, with the bedding surfaces being smooth and flat depending on the grain size of the rocks. Grain bond varies from poor to good. In the gallery and east portal area, a loose rock overburden with hlang debris, hanging sand, and weathered rock is present, which occurs up to 7 m thick in total. The rock here is strongly loosened and deconsolidated and can be classified in the "sand" fraction.

The gradient of the tunnel lies above the main groundwater level, which is at least 20 m below the gradient in the route area. Depending on the occurrence of fine-grained siltstones or mudstones, however, suspended groundwater levels could be encountered, which could lead to temporary water ingress when piercing these layers or approaching large gaps.

2.2 Supporting structure, sealing

The 899.5 m long Lionheart Tunnel is divided into 2 sections, which differ fundamentally in their supporting structure and construction method. Whereas the western section with a length of 495 m could be constructed as a gallery using the open cut method, the eastern section with a length of 404.5 m had to be built using the closed cut method. The maximum ridge overlap of the tunnel is about 52m. The retaining walls required in the portal areas due to the steep incline of the existing slope were designed in the shape of shells for design reasons. In addition to the retaining walls, the entire gallery and the tunnel portals are also characterized by a special design under the guiding principle of dealing with the natural forms of the Palatinate Forest.

The cross-section chosen was the standard RQ 12 t cross-section with a carriageway width of 7.50 m including verges, consisting of 1 directional carriageway each, and the 1.0 m wide emergency walkways on both sides with a width of 9.50 m. The cross-section of the tunnel was designed in accordance with the principle of the "RQ 12 t". The cross-sectional shape of the tunnel is fully adapted to the local geological conditions and therefore changed depending on the construction method and the geological formations encountered.

Where the tunnel could be constructed using the cut-and-cover method, a closed vault cross-section on a flat base slab was used. In the course of mining, a closed basket arch cross-section with invert vault was selected in the excavation areas of the tunnel entrances. In the stable rock, it was possible to dispense with the invert vault. The inner shell of the mining tunnel was designed with a thickness of 40 cm, while the open tunnel areas were constructed with a shell thickness of d =60 cm.

The retaining walls were constructed as flat-bottomed gravity walls or angular retaining walls with a facing in natural stone analogous to the gallery and tunnel portals.

The gallery has openings on the valley side of approx. 3.0 m height from the upper edge of the 1.1 m high parapet, which is rounded in cross-section and also serves as a protective wall. In the transition area to the tunnel, the parapet rises and thus gradually closes the gallery openings. For the valley-side foundation of the gallery, 4 piles 0 1.20 m were required for each 10 m gallery block. A parapet was placed on top of the piles, which on the one hand catches falling earth and on the other hand forms a frame with the piles on both sides, which is statically necessary.

All structures of the Lionheart Tunnel (tunnel, gallery, portals and retaining walls) are located above the main groundwater level, so that pressurized water-retaining seals were not required. The tunnel was waterproofed by means of a single-layer sealing layer of plastic sheeting placed between the shotcrete lining and the tunnel inner lining, and an upland water drainage system running along the base of the cross-section. All parts of the tunnel and gallery constructed using the cut-and-cover method were also sealed with a plastic sheeting that adjoined the mining waterproofing.

2.3 Operating facilities, equipment

Since the portal distances between the Barbarossa and Lionheart Tunnels are only about 200 m, an operations center was built at the eastern portal of the Lionheart Tunnel to house all the equipment required for the electrical supply and ventilation of both tunnels.

In addition to the 20 kV system, the transformers and the battery system for uninterruptible power supply, the control center houses the entire switchgear. The entire tunnel is automatically controlled and partially remotely monitored. All emergency calls and the activation of fire alarms are transmitted to the police, from where the fire department can be alerted.

Power is supplied from the high-voltage network by means of a 20 kV ring cable looped into the operations control center. The control center contains installations for the mains supply and the uninterruptible power supply, which operate the safety systems, the fire alarm system, the indication lights, the measuring and control systems and the night passage lighting.

The tunnel was equipped with longitudinal ventilation consisting of jet fans. For this purpose, a total of 6 jet fans are installed in pairs in the tunnel. The longitudinal ventilation is controlled by means of carbon monoxide and visual opacity measuring devices, which are distributed at points throughout the tunnel. In the event of a fire, an automatic fire ventilation program ensures optimum removal of the smoke plumes via the tunnel portals, depending on the source of the fire.

 The tunnel is illuminated by high-pressure sodium lamps in a single-row arrangement, which are positioned off-center to the tunnel axis for maintenance reasons. The adaptation section, the area where road users' eyes have to adjust to the changed lighting conditions, received backlighting, while the interior section received mixed contrast lighting. Artificial lighting is limited to the closed part of the tunnel; the gallery areas serve as a natural adaptation section. Luminance meters in front of the portals are used to switch the required adaptation distance fully automatically in various stages depending on the outside brightness.

In the tunnel, 6 emergency telephones are provided, which are installed in wall niches. When the niches are opened, a flashing light is switched on and this is displayed in the police station. In addition, there are manual fire alarms in the emergency call niches, 2 6 kg dry extinguishers accessible to drivers and a hydrant connection for the fire department.

Approximately in the middle of the tunnel, one breakdown bay is available for each direction of travel. The breakdown bays are located opposite each other so that vehicles can turn around in an emergency.

A traffic control system with variable message signs and signal systems is installed upstream of the tunnel. Various traffic programs can be called up, ranging from speed reduction in the event of incidents in the tunnel to full closure by signal heads. In the event of fire or obstruction, emergency programs are initiated fully automatically.

2.4 Construction method

In accordance with the geological conditions, tunnelling using the shotcrete method was chosen for the excavation of the tunnel, as this allows the different rock conditions to be taken into account relatively well without having to change the construction method. Only the type and method of rock solution, the necessary securing means and the driving cycle varied within the geologically and hydrologically different areas. In the hard rock, excavation was carried out by blasting, in the unconsolidated rock by hydraulic excavators.

The excavation of the total cross section was carried out in at least 2 partial excavations, consisting of the "calotte" (upper cross section part) and the "hawser" (lower cross section part). If a bottom arch had to be installed for structural reasons, the cross section was extended by another partial excavation, the "sole".

The total cross-section to be excavated has an area of 79 to 94 m2 , depending on the geological conditions encountered.

Directly after blasting or excavation and immediately after removal of the excavated material, the exposed rock faces were supported by a safety shoring system in accordance with the rock mechanics and tunnel construction requirements. This shoring, which stabilized the rock until the subsequent installation of the tunnel lining, consisted mainly of shotcrete, reinforcing steel meshes, steel anchors, steel spiles and steel tunnel arches in the required dimensions and combinations.

In the mining area, the sealing was first tacked to the support with an intermediate layer of protective fleece so that the 40 cm thick inner lining could then be counter-concreted using a formwork carriage.

For those tunnel sections which, like the entire gallery, were constructed using the cut-and-cover method, excavation pits with slope protection had to be created.

3. Construction execution

The construction work was awarded by public tender on the basis of the tendered structural design; no special proposals were used.

The excavation pits required for the construction of the gallery were excavated step by step, starting from the west, and then secured with soil nails and shotcrete due to their steep slopes. At the same time, the piles for the foundation of the gallery supports were installed.

The excavation of the excavation pits and thus the construction of the building components using the cut-and-cover method was continued until sufficient rock cover and stable geological conditions were encountered to permit further excavation by mining. In accordance with the New Austrian Tunneling Method (NOT), the excavation of the entire cross-section was carried out in 2 partial excavations, starting with the calotte and, after securing it, continuing with the excavation of the bench. These operations were carried out one after the other along the entire length of the tunnel in one direction.

Depending on the geology, 2 types of excavation were used. In the area of rock, the rock was loosened by blasting. The excavation was carried out by detonating blasting cartridges, which were inserted into individual boreholes distributed over the cross-section to be excavated. The depth of the drill holes used to determine the excavation length depended on the rock conditions encountered and varied between 1.0 and 2.5 m in the calotte and between 2.0 and 5.0 m in the drift.

The unconsolidated rock, on the other hand, was excavated with hydraulic excavators, whereby the partial excavations of the cross-section were short-staggered in the longitudinal direction, excavated immediately one after the other and immediately secured. Depending on the rock behavior, the cut-off lengths in this type of excavation were 0.7 to 1.0 m in the calotte and 0.7 to 2.0 m in the bench.

The resulting usable excavated material could be transported away for installation in the dam section at Queichhambach, while the unsuitable material was used to improve reforestation areas. Part of the masses served as backfill material for the sections of the structure to be constructed using the open cut method.

In the open cut section, after excavation, the construction of the reinforced inner shell of the gallery (d = 0.60 m) was started in sections (blocks) of 10 m. The reinforced inner shell of the gallery (d = 0.60 m) was placed in the open cut section. Subsequently, the 2 mm thick plastic sheeting was laid around the concrete as a seal and secured by protective concrete or masonry as a seal protection.

The work sequences for concrete removal in the mining area had to be carried out in exactly the opposite way and consisted of the following 5 phases after completion of the securing work:

  • Profile check
  • tacking of the waterproofing to the protection
  • Reinforcement of the inner shell
  • concreting of the 40 cm thick inner shell with formwork carriage
  • post-treatment.

Finally, work was carried out to complete the tunnel (drainage, roadway construction, equipment) and the gallery including retaining walls (natural stone facing, sound-insulating cladding in the portal and gallery areas) as well as recultivation of the construction site.

The Löwenherz Tunnel, the gallery and the retaining walls are a very complex engineering structure in terms of design, which is not typical for road tunnels and must be regarded as an individual case.

4. Literature

[1] Landesamt für Straßen- und Verkehrswesen Rheinland-Pfalz, Straßenprojektamt Dahn - Bad Bergzabern: Broschüre Neubau der Bundesstraße B 10

[2] Straßenprojektamt Dahn - Bad Bergzabern: Entwurfs- und Ausschreibungsunterlagen

 

  • Country: Germany
  • Region: Rheinland-Pfalz
  • Tunnel utilization: Traffic
  • Type of utilization: Road tunnel
  • Client: BRD, Straßenverwaltung Rheinland-Pfalz
  • Main construction method: Open/Trenchless
  • Type of excavation: In-situ-conrete/Shotcrete
  • No. of tubes: 1
  • Tunnel total length: 899.5 m, incl. gallery 495.0 m
  • Cross-section: Gallery 75 m², Tunnel 79-94 m²
  • Contract Volume: 40 mill. plus 4.2 mill. furnishing DM
  • Construction start/end: 1991-1995 (45 month)
  • Opening: June 1995