1. General

In Porta Westfalica, the federal highway B 61 runs through a landscape of Germany that is worth seeing and is unmistakable in its kind. Here the river Weser pierces in a narrow place the mountain ranges of the Weser mountains in the east and the Wiehen mountains in the west, which act like a barrier. On the eastern slope of the Wittekindsberg stands the Kaiser-Wilhelm-Denkmal, built from 1892-1896.

The existing traffic conditions in this area were unbearable for the road users and residents. For example, about 25,000 vehicles/day were on the two-lane B 61 in the Barkhausen district in the middle of a densely populated residential area. The B 61 is a road running in a north-south direction and is of supra-regional importance, connecting the areas of Dortmund-Lunen, Bielefeld and Bremen.

The Porta Westfalica represents a breakthrough created by the Weser River from the Weserbergland to the North German Plain. On the right bank, the Jakobsberg towers close to the river, while on the left rises the Wittekindsberg with the majestic Kaiser Wilhelm Monument. Early on, roads led to the right and left of the Weser into the North German lowlands and on to the sea. Later, the railroad - today with the 4-track line Hanover-Hamm - was added.

Due to the spatial narrowness to the right and left of the Weser breakthrough through the Weser/Wiehengebirge mountains, the B 61 between Bad Oeynhausen and Minden runs largely within the built-up area of the town of Porta Westfalica.

The B 61 n runs in the southwest of the Barkhausen district of the town of Porta Westfalica and swings north from the old course of the B 61 with a left-hand curve and then runs roughly parallel to the Weser through Porta Westfalica.

After being linked to a new bridge over the Weser, a 1,730 m long tunnel section begins in the Weser floodplain to the east of the residential area of Barkhausen. The tunnel ends around 750 m before the junction with the B 65. The route then runs east in the urban area of Minden parallel to the residential development 'Zollern' and ends at the B 61 - Ringstraße with a distributor circle that takes in the B 61 n old, the B 61, the B 65 and the L 534.

For this purpose, the two-lane Weser bridge in the Porta was demolished and replaced by the new construction of a two-lane Weser bridge (with linking lanes, four-lane) shifted to the south, which establishes a connection between the B 61 on the left and the B 482 on the right of the Weser.

The direct routing of the new Weser bridge (B 61) into the Kirchsiek (L780 )eliminated the offset at the Hausberge junction with its well-known frequent traffic jams.

2. Construction design

The Weserauentunnel itself consists of three parts:

• the southern trough-shaped ramp 310 m long,
• the 1,730 m long tunnel, which plunges deep into the groundwater, and
• the northern trough-shaped ramp of 520 m length.

The total length of the structure is 2,560 m.

In the area of the tunnel, the B 61 n has a curved line in plan with a clothoid of A = 516.628 and circular arcs with R = 900, 6000, 3000 and 5000 m. The longitudinal section has gradients and steeps.

The longitudinal section has gradients and slopes ranging from 0.03 to 1.32%.

2.1 Geology and hydrology

The Weserau tunnel is located in the terrace deposit of the Weser River, at the low mountain sill of the Weser and Wiehen Mountains. Under the topsoil there is a 30 cm to 4.00 m thick alluvial loam layer, followed by widely graded sand and gravel mixtures with intercalated gravel banks. The base is formed by a bedrock of Porta sandstone, which dips from south to north from 10 m to 60 m depth. The groundwater levels in the Porta Westfalica area are determined by the Weser water levels. Due to the high water permeability of the soil, the groundwater levels are promptly corrosponding to the Weser water level.

2.2 Construction

The tunnel was constructed as a two-cell frame in an open excavation. The construction supports (lateral sheet pile wall, excavation pit anchors, vibrating injection piles and underwater concrete base) are not connected to the structural component.

For the structural condition, the building supports were designed for the 10-year flood, so that appropriate measures had to be taken if this flood mark was exceeded. For this case, the controlled flooding of the excavation pits was planned in an "emergency concept".

Fortunately, the construction team was spared this, although the Weser came within a few centimeters of the critical high-water mark during the construction period.

The Weser river tunnel is essentially designed and dimensioned according to the current principle of the "water-impermeable concrete structure" (WUB-KO) in accordance with ZTV-Tunnel, Part 2. For this purpose, the requirements for impermeability were defined according to ZTV-Tunnel and specified with impermeability class 2. For the verification of the crack width limitation, the permissible calculated value of the crack width was defined as wk^, = 0.15 mm for the wall and wk = 0.25 mm for the floor and ceiling. To reduce the heat of hydration, a special concrete mix design was provided with the addition of 60 kg/m3 of fly ash. The block length of the individual structure sections is 15 m, in deviation from the ZTV Tunnel. The block joints were produced as space and compression joints, with the inner joint band being provided with vulcanized steel straps and injection hoses on both sides. The joint inserts as well as all other installed parts had to comply with building material class A (non-combustible) according to DIN 4102. Here, the sheet connects two adjoining blocks (with the joint tape) on the one hand and the tunnel floor with the rising walls on the other. The minimum concrete cover is 5 cm.

For fire protection, the tunnel floor has an increased concrete cover of 6 cm, in which additional fire protection reinforcement, 3 cm from the inside, was placed in the form of a structural steel mesh. This fire protection reinforcement is galvanized for corrosion protection reasons and connected to the structural reinforcement by S-hooks.

The structural reinforcements are separated from the structural concrete cross-section and were not included for buoyancy safety in the service condition.

For the final condition, the buoyancy safety is available with n ^ 1.1, whereby the calculation basis for this was the Weser hydrographs with the HHW of 1946.

The concrete pavement of the tunnel structure and the northern and southern ramp areas were sealed with a 16 cm thick pavement structure.

This pavement structure consisted in detail of:

• 0.5 cm sealing layer consisting of a bituminous welded sheet or by means of liquid plastic, as well as a sealing or scratch filler layer
• 3.5 cm mastic asphalt protective layer
• 4,0cm Bitu base course
• 8.0 cm asphalt fine concrete surface course

In addition, 1.00 m to 2.00 m wide reinforced concrete caps were formed for the emergency walkways within the tunnel construction project.

2.3 Operational equipment

The tunnel is equipped with adaptation lighting, passage lighting and emergency fire lighting. The adaptation lighting consists of three groups of lamps, one of which is continuously controlled and the other two groups are switched on as required.

The drive-through lighting also serves as safety lighting and is equipped as mixed contrast lighting with a maximum roadway luminance of 4.2 cd/m2 during the day, which is lowered to 0.8 cd/m2 at night.

In the event of a fire, emergency fire lighting has been provided as an orientation aid at a distance of approx. 22.5m.

The tunnel ventilation is designed as mechanical longitudinal ventilation with jet fans. The design criterion is the case of fire, for which up to 16 fans may be required.

In consideration of the possibility of two-way traffic in exceptional cases and the provision of reserves for fire, 20 fans were installed per tunnel tube. The fans are arranged in four groups of five per tube.

A tunnel radio system is installed in the tunnel for BÖS and for the operational service. Furthermore, it is possible to receive a radio station with traffic radio, which can also be used to address the road users in the tunnel.

It is also possible to address road users in the tunnel via an electro-acoustic announcement system.

In each tunnel tube and the ramp areas in front of it, there are 15 emergency call stations at intervals of approx. 150 m, which are equipped with hand-held fire extinguishers. From there, emergency calls can be made to the regional traffic control center in Arnsberg.

To monitor traffic safety in the tunnel and in the area of the ramps, 26 video cameras have been installed, 13 in each tube at intervals of approx. 150 meters.

A fire inside the tunnel tube is automatically detected and localized by means of a temperature-sensitive sensor cable (Fibro Laser) or via visual opacity meters.

Manual push-button detectors are provided in the emergency stations.

These fire alarms are not automatically reported to the fire department's control center, but are evaluated using visual monitoring, and if a fire is detected, an alarm is triggered from there.

In the Weserau tunnel, there is a fire extinguishing system with an external extinguishing water tank with a capacity of 72 m3 .

Hydrants, each with two connections for B hoses, are provided in niches in the center wall at intervals of approx. 150 m. The hydrant niches are accessible from both tunnel tubes.

For congestion detection, induction loops and radar sensors are installed at intervals of approx. 400 m in each direction of travel.

Traffic is influenced by variable message signs in LED technology in front of the portals, in the tunnel and at the connections.

Tunnel closures are indicated by variable message signs with additional half barriers.

Electrical power will be supplied from the public grid. For the greatest possible supply security, the connection is made via a ring and stub feed.

The entire system is controlled and monitored by the central control system. Four CO measuring points and four visibility measuring points are provided for each tunnel tube to control the ventilation.

To control the roadway luminance level, the ambient luminance is measured at each portal and the roadway luminance in the viewing sections.

The operations building, as the central control center for the operation of the Weserau Tunnel, was built directly next to the tunnel alignment and is directly connected to the tunnel structure via an accessible cable duct in the ceiling 4.

The operations building has an irregular ground plan. The main building, which has a basement and several stories, mainly houses the emergency power supply and the technical equipment and facilities, while the single-story annex, which does not have a basement, houses the control room and the staff rooms.

Furthermore, a cylindrical elevated tank was built directly next to the operations building to hold the required 70 m3 of extinguishing water.

The Weserau tunnel can be exited to the outside at the respective third points of the two 1,730 m long tunnel tubes through the stairwells of the emergency exits located in the emergency stop bays.

The surface water from the north and south access ramps is fed into the pump houses built next to the portals directly in front of the tunnel start and end.

These pump houses consist of an underground rectangular basin with an earth cover, with a useful volume of 210 m3 in the north pump house and 80 m3 in the south pump house, as an intermediate storage tank and a pump shaft.

3. Construction

The 2,560 m long construction project was built as a line construction site. The structure was built in 15 dry docks. These dry docks had a maximum length of 200m. The entire structure, consisting of 162 construction sections, was built in sections in these open excavation pits, whereby 150m of the southern ramp had already been built in a previous construction project.

Intensive construction scheduling was required for this complex work.

After removal of the topsoil, a construction road was built within the construction area. This construction road served to shift construction traffic into the construction site so that approx. 120,000 truck transport trips did not burden the adjacent residential neighborhood.

During the subsequent sheet pile work, the 14 to 18 m long double piles were vibrated in by vibratory driving. In areas where buildings were close by, the substance of the building was documented by a survey of evidence on the one hand, and the vibration was measured on the other. Subsequently, the existing alluvial clay was removed separately and temporarily stored at the construction site.

After driving the sheet piles, the waling was continuously installed for sheet pile stiffening. In the process, the grouted anchors were produced as temporary anchors. The excavated gravel/sand was transported within the construction site, processed and transported to the on-site concrete plant. During this process, the excavation depth below the water table was controlled with rotary lasers during soil excavation.

To prevent the risk of contamination or soil entrapment during the installation of the underwater concrete, the sheet piles were cleaned by high-pressure water jetting.

The "fine subgrade" of the excavated soil was produced by means of suction cutterhead pumps so that the contractual requirement of an evenness of ± 10cm to the target was met.

This verification was carried out by means of a predefined measuring procedure, with a specially prepared boat equipped with GPS and echo sounder serving as the measuring station.

The center injection piles used were a special form of vibrated (grouted driven steel) injection piles, which were assigned to DIN 4026.

The underwater concrete base was calculated as a vault structure, with load case 2 as the standard case in the calculation and the failure of a pile as load case 3. The load transfer between sheet pile wall and underwater concrete base was calculated via friction. On this basis, the underwater concrete base was produced in thicknesses ranging from 90 cm to 1.00 m.

The concreting sections were divided into daily outputs between 1200 m3 and 1400 m3, with an hourly output of the on-site concrete plants of 1 00-110 m3. The underwater concrete was produced by two stationary site mixing plants using submersible equipment, transported by concrete trucks and transferred to the concreting pontoon via a concrete pump. The concrete was placed via this force-guided pontoon using the contractor method.

After the excavation had been lightened, the concrete surface was cleaned of residual sediment and cement slurry, and the protruding Rl pile heads were burned off. Subsequently, a level check of the underwater concrete base was carried out and a base deepening for the longitudinal drainage pipe was milled.

The tunnel structure was constructed in block sections of 15m.

When producing the plates of the joint construction, care was taken to ensure that the distance between the plates was at least 5 cm (2.5-faehe grain size) so that no circulation could occur. As in the rest of the tunnel, the aim was not only to achieve watertightness, but at the same time to limit cracking.

The excavation pit could be constructed without a working chamber, since the structural tunnel cross-section was concreted "directly" to a filigree slab (as a lost outer formwork in front of the sheet pile wall). This working method had the advantage that no formwork ties penetrated the outer walls.

The inner formwork skin of the structural tunnel cross-section was created by a formwork carriage, of which two were in use as construction progressed.

These formwork carriages were designed in such a way that they could be moved in and out and moved under their own power via hydraulics.

Due to the dead weight of 1,4001, each formwork carriage was heavy enough to withstand the concrete pressure without further anchoring, especially since a concrete climbing speed in the walls of > 2.50 m/h was specified.

The outer wall reinforcement was produced in advance and then formed with the incoming formwork carriage. The center wall was also reinforced in advance, and the required empty pipes for the operational equipment were laid at the same time. The formwork carriage was moved into the wall reinforcement prepared in this way and then the floor reinforcement, including the fire protection reinforcement, was laid.

The wall and slab concreting of a tunnel block was carried out with two concrete pumps and an additional reserve pump, as well as a concreting crew that was adequately manned and increased for stripping and smoothing. Two to three vibrators were used in each concreting area.

After completion of the concrete work, the sheet pile wall chord was removed and the anchors cut so that the sheet piles could be pulled again and reinstalled.

The piles were installed three times in the 2,560m long construction section. The sheet pile valleys between the filigree slab and the sheet pile wall were backfilled with gravel sand before pulling. This ensured that, on the one hand, no cavities were created during drawing and, on the other hand, the surface water could flow unhindered through the gravel sand to the groundwater.

The tunnel top was protected with an epoxy resin primer on which a sealing layer with a bitumen welding sheet was applied. On top of the sealing layer, a 10 cm thick concrete protection layer was placed for protection, which received a structural reinforcement.

On top of the concrete protection layer, the tunnel was covered with a 1.20 m thick soil backfill and a 0.30 m thick topsoil cover.

Subsequently, the carriageway structure was constructed in the tunnel.

After completion of the tunnel's shell in 2001, the tunnel's operational equipment was installed. Before the tunnel was put into operation in December 2002, fire tests were carried out in the tunnel to check the safety equipment and the ventilation system.

 

 

• Country: Germany
• Region: North Rhine Westphalia
• Tunnel utilization: Traffic
• Type of utilization: Road tunnel
• Client: Federal Republic of Germany, Land of North Rhine Westphalia
• Consulting Engineer: Holzmann AG, ELE Erdbaulaboratorium Essen, Landschaftsverband Westfalen-Lippe, WSBA Minden
• Construction Monitoring: Landschaftsverband Westfalen-Lippe, WSBA Minden
• Contractor: Bilfinger Berger AG, Köster AG
• Main construction method: Open
• Type of excavation: Open (dry docks)
• Lining: Concrete formwork
• No. of tubes: 1
• Tunnel total length: 1,730 m
• Cross-section: 154 m² as standard cross-section
• Contract Volume: approx. € 83 million
• Construction start/end: September 1998- May 2001
• Opening: December 2002