1. General

With the new construction of the federal freeway A 44 between Meerbusch and Düsseldorf, the last section of the freeway quadrangle around the state capital Düsseldorf has been completed.

The overall measure of the Rhine crossing in the course of the A44beillverich comprises three large engineering structures: the Strümp Tunnel, the Rheinschlinge Tunnel and the Rhine Bridge. The two tunnels are described below.

At the start of construction, the route of the A44 ended on the left side of the Rhine with a temporary junction with the B 222 federal highway in Meerbusch-Strümp at construction km 4+050. This temporary junction was integrated into the various construction phases in order to maintain the B 222 federal highway to the A 57/44 interchange. The actual construction of the new freeway began at construction km 3+100 at the L 386 underpass. On the right-hand side of the Rhine, the Düsseldorf Messe junction was built with the exit ramp to the trade fair in the direction of Mönchengladbach and the entrance ramp in the direction of Velbert/Düsseldorf Airport. In addition, part of the embankment fill to the eastern Rhine bridge abutment had been backfilled. The expansion therefore ends at construction km 9+550. Two tunnels and one bridge had to be built between the start and end of construction. The total construction distance of 6.4 km is divided into 3,845 m of artificial structures and 2,555 m of free section; the latter was mainly constructed in embankment position.

The Strümp tunnel structure, which consists of the main tunnel with troughs for the A44 and additional trough and tunnel structures for the ramps as well as enclosures for the carriageways of the entrances and exits of the junction, begins at construction km 3 + 530 and ends at construction km 4 + 570.

The main tunnel with a length of 1,040 m consists of the following structures:

• western trough structure

km 3+530.0 to km 3+595.0

(I - 65.0 m)

• tunnel

km 3+595.0 to km 4+243.5

(I = 648.5 m)

• Eastern trough structure

km 4+243.5 to km 4+570.0

(I = 326.5 m)

Additional engineering structures are required in the area of an Old Rhine loop at km 3+600. Here, the western tunnel portal including the northern approach to the Strümp interchange and the southern exit from the Strümp interchange had to be covered for reasons of landscape design, ecological connectivity, noise protection and to create a pedestrian and bicycle crossing.

The tunnel structure Rheinschlinge with a length of 1520 m, which consists of the main tunnel with troughs, starts at construction km 5+190 and ends at construction km 6+710 and is divided as follows:

 

• western trough structure

km 5.190 to km 5.505

(I =315.0 m)

• tunnel

km 5.505 to km 6.375

(I = 870.0 m)

• eastern trough structure

km 6.375 to km 6.710

(I = 335.0 m)

The tunnel and trough structures were to be integrated into the landscape in such a way that the natural terrain horizon was preserved as far as possible. Newly created embankment areas were designed in accordance with the "accompanying landscape conservation planning" and provided with earth embankments in the area of the raised tunnel portals.

The design of the tunnel portals in terms of position and shape was adapted to the landscape and therefore produced with a sloping tunnel approach and a clear widening of the tunnel mouth.

2. Structure design

2.1 Location and cross section

Tunnel Rheinschlinge

The alignment of the 6-lane highway in the area of the structure is carried out in the direction of stationing from west to east in the sequence: clothoid A = 850 m (western trough area), clothoid = 900 m, right-hand curve R = 2,600 m, clothoid A = 1,000 m, straight line. The straight section begins about 74 m before the end of the tunnel and continues along the eastern trough. Deviating from the standard cross-section, the following cross-section was specified for each directional carriageway, which corresponds in total width to a cross-section 33T according to the RABT:

• emergency walkway                                                  1.00 m
• hard shoulder                                                               2.40 m
• shoulder                                                                         0,30 m
• 3 lanes a 3.50 m                                                            10.50 m
• shoulder                                                                         0,30 m
• emergency walkway                                                  1,00m

Total 15,50m

Tunnel Strümp

Consisting of western trough, tunnel and eastern trough. The entire route is an arc of a circle with R = 1,500 m, with a transitional arc A = 500 m only at the eastern end. The cross-section corresponds to that of Tunnel Rheinschlinge.

2.2 Geotechnical conditions

The construction area of the A44 Rhine crossing between the Strümp junction on the left bank of the Rhine and the Düsseldorf-Messe junction on the right bank of the Rhine belongs to the Lower Rhine Bay over a large area. According to information from geological maps, the deeper subsoil here consists of Tertiary sediments that were formed near the coast about 30 million years ago during the Upper Oligocene period and reach a thickness of more than 100 meters. On top of these marine sediments -fluviatile sediments of the lower terraces of the Rhine stream in the form of gravels and sands were subsequently deposited during the Quaternary period. The transition area between Quaternary and Tertiary sediments has been stressed by glacial processes, the Tertiary subsoil has thus been pre-stressed by glacial processes. The termination of the geological profile towards the ground surface is formed by a Quaternary cohesive overburden, generally known as floodplain loam or floodplain clay. Within this cover layer, silted-up areas of former meanders of the Rhine are present in recent times as so-called Rhine loops, in which the cohesive soils show higher organic contents and softer consistencies according to their origin and the lower age.

With regard to hydrogeology, the Quaternary gravel and sand layers represent the aquifer in the area under consideration; the underlying Tertiary fine sand layers have a much lower water permeability and can then be described as "groundwater inhibitors". The Quaternary overburden near the surface has an even lower permeability and in many cases lies above the groundwater table, so that it can be described as a "groundwater non-conductor". Groundwater transport thus takes place predominantly within the Quaternary gravel and sand layers. The groundwater levels of this GW conductor are influenced by the Rhine water levels in large areas of the construction area; in addition, precipitation-dependent, seasonal as well as long-term fluctuations are present. At mean groundwater and Rhine water levels, the groundwater flow direction is from southwest to northeast towards the Rhine.

The tunnels cut into the aquifer and thus form an obstacle in the groundwater flow which, in the worst case, is approached almost vertically and is thus flowed around, under and over according to its shape and variable depth.

2.3 Construction

The tunnel and ramp cross-sections were designed as a "white tank". For the tunnel slabs, this did not apply in the areas that were outside the road crossings and where the earth overburden was at least 1.0m. Here, a bituminous seal with protective concrete was applied for reasons of protection against chloride ingress from de-icing salts and as root protection.

The spacing of the expansion joints is 7.50 m in the ramp area and 10.0 m in the tunnel area in accordance with the lower constraining loads. The expansion joints are sealed with circumferential, internal elastomeric expansion joint tapes with vulcanized steel straps. Injection hoses are attached to the ends of the steel straps and are routed into the tunnel interior on the walls above the carriageway or just below the ceiling to allow subsequent sealing of the anchoring zone of the joint tapes by injection if leaks are detected. The inner sides of the expansion joints are closed by FFM 7/3 waterstops. The construction joints between the outer walls and the base slab or tunnel ceiling are secured with internal construction joint waterstops with vulcanized steel straps.

Subsequent injection via injection hoses is also possible with the construction joint tapes. The injection hoses are routed to the outside in the interior and exterior walls above the walkway and below the floor slab on both sides of the expansion joints, where they are accessible via storage boxes.

To protect against spalling on the tunnel ceiling in the event of fire, galvanized mesh reinforcement was installed in addition to the load-bearing reinforcement.

2.4 Tunnel safety and tunnel operation

Each of the tunnels includes a tunnel operation building that houses the pumping equipment as well as monitoring and control systems for the tunnel installation.

Maximum safety for road users is ensured by the use of state-of-the-art technology. During normal operation, computer-monitored plant electronics ensure, among other things, optimum roadway lighting and fresh air supply, as well as drainage in the low-lying areas. For emergencies, automatic fire alarm systems, fire extinguishing systems, emergency call stations, escape doors and a dual power supply were installed. Fire extinguishing systems were installed at 170 m intervals, and fire detection is provided by a linear heat detection system under the tunnel ceiling. Emergency call facilities in the tunnel are installed every 170 m in the area of the fire extinguishing niches. Video surveillance is possible via 44 cameras in the tunnel and outside areas. Traffic detection on the track, ramps and in the tunnel area is carried out via induction loops and evaluated by the tunnel control system and traffic control center. Three escape doors per tunnel tube and the portals in the center walls are available as escape routes. Illuminated escape route markings installed at intervals of 25 m are used to locate these escape routes.

Large-scale planted infiltration ponds with settling and oil separation basins built into the ground and integrated into the landscape take care of the collected water. Normally, this water is piped to the tunnel's low point and then pumped to the nearby seepage system, as is the case with the Strümp Tunnel, which has its low point in the area of the junction. In the case of the Rheinschlinge tunnel, which is located in the area of the nature reserve, a greater technical effort had to be made. The water is pumped from the low point via an additional pumping station to the operating building outside the nature reserve and from there via a pressure line to the infiltration facility. The llverich-Rheinschlinge nature reserve is protected.

3. Construction

3.1 Construction method

The hydrogeological boundary conditions were decisive for the various construction stages. In order to minimize the impact on the nature and landscape conservation areas and the water protection zones of the nearby Meerbusch-Lank-Latum waterworks, only "groundwater-friendly" construction methods were considered. According to the preliminary study, open construction methods were to be preferred to closed construction methods for solutions comparable in terms of traffic, both economically and in terms of technical feasibility. For the design, therefore, the construction of excavation pits with tight sheet pile shoring was recommended, since the shoring had to be removed as completely as possible to restore the required groundwater flow paths in the final state. To protect the groundwater, the shoring walls had to be embedded sufficiently deep in the tertiary fine sand layer acting as a groundwater inhibitor in any case. In this case, with practically tight retaining walls, only the groundwater pushing through the low permeability groundwater inhibitor of the excavation pit from below had to be absorbed by means of an internal dewatering system.

Since a watertight enclosed excavation completely stops the groundwater flow in the subsoil at this point during construction, the hydrogeological investigation revealed a maximum permissible length of a so-called "construction dock".

3.2 Shoring

The possibility of driving and pulling sheet pile sections more than 20 m long was investigated in the course of the design planning by test pile driving. In the course of this, penetration depths of more than 8 m in the dense to very dense tertiary fine sands were achieved using the vibrating method with low-pressure flushing as a driving aid, and the piles could be recovered without difficulty after a service life of about half a year.

The excavation concept for the 15 m deep main excavation pits of the tunnel and trough sections was a sheet pile shoring system tied back with injection anchors. The watertight sheet piles, which are up to around 22 m deep, tie into the much less permeable tertiary fine sand horizons and block off the free groundwater in the more permeable quaternary strata above.

Up to three anchor layers with anchor lengths between 10 and 19 m and service loads of up to 880 kN in the Quaternary and up to 770 kN in the tertiary fine sands were produced.

The execution of the injection anchors was a special technical challenge, especially in the two lower anchor layers, since these anchors had to be drilled and set against water overpressure (approx. 10 to 12 m water column).

In order to ensure a continuous workflow of the shoring, excavation and carcass works, the 240 m long excavation pits in both tunnels were divided into approx. 80 m long partial excavation pits by means of transverse bulkheads. In this way, it was possible to backfill the last 80 m of the total excavation pit and remove the shoring in a kind of rolling system, while work could be continued in the remaining 160 m. The next 80 m were then excavated in the direction of work. The next 80 m of shoring was then placed in the working direction. Excavation, dewatering and anchoring work were coordinated in such a way that the shell construction did not come to a standstill in the open, excavated sections of the excavation pit.

The sheet piles were pulled again after completion of the shell construction and backfilling work once the structure had reached buoyancy safety, so that the groundwater flow was no longer interrupted.

3.3 Dewatering

There are no normative rules for lowering groundwater levels to drain excavations and for the dewatering equipment to be installed for this purpose. These measures depend on the subsoil conditions (soil mechanical, geological, hydraulic conditions), the inflowing water volume from the groundwater-bearing strata and the drawdown target in connection with the excavation geometry. The dewatering to be installed had to be adapted and dimensioned to these parameters in each case.

The installed temporary residual dewatering mainly consisted of gravity wells, vacuum deep wells and a system of drainage trenches and pump sumps.

The gravity wells were tasked with capturing and pumping out the groundwater located in the gravels and sands. The underlying Tertiary fine sands in the Tunnel Rheinschlinge area were dewatered by gravity wells. Because of the significantly lower water permeability, these wells were sealed off from the Quaternary strata and then placed under vacuum.

The water in the less permeable fine sand was sucked to the wells by vacuum impingement. The vacuum deep wells were installed to collect the groundwater seeping through the excavation over a wide area. The average pumping capacity of a vacuum well was about 3 m3/h.

3.4 Structural design and cycle construction

First, the inverts of the ramp and tunnel blocks were constructed. The thickness of the invert of the ramp blocks increases from 0.50 m at the ends of the structure towards the tunnel portals to a thickness of up to 4.0 m in order to achieve sufficient buoyancy safety here. In the control area of the tunnel blocks, the thickness of the invert slabs is 1.20 m on average. The invert slabs were provided with grooves at right angles to the tunnel axis on the underside in order to achieve interlocking with the ground. This prevents the tunnel blocks from sliding in the longitudinal direction of the tunnel due to the reduced friction caused by the above-mentioned double PE foil. Together with the invert slabs, the beginners of the tunnel walls were concreted, which also accommodate the longitudinally running, internal construction joint strips. Integrated into the invert slabs are the pipes and manhole bases of the structure drainage and the drainage collection shafts.

The construction of the walls followed with a lag of two block lengths in relation to the inverts. For their production, formwork was provided for one block, i.e. for a center wall and two outer walls. Thus, like the bottom slab, the walls were continuously advanced. The otherwise constant wall cross-section of 1.00 m wall thickness was interrupted by recesses or reinforcements for the emergency call niches, fixtures for fire extinguishing and rescue equipment, escape doors, ventilator niches, the external haunches for connecting the sheet piles of the transverse bulkheads and the niches for accommodating the noise protection elements in the portal areas.

The duration of the work cycle was determined by the time required to produce the floor slabs. The surface of the floor slabs has a roof profile with an average thickness of 1.20 m in standard cross-section. The floor slabs were produced on formwork carriages with three panels trailing the walls. The slab formwork for one tunnel block was provided in each case. The formwork was raised by a total of 3cm to compensate for the slab deflection and to achieve a slight optical protrusion in the standard block.

In addition to the increased design effort in the area of the expansion and construction joints, the rules for concrete production and processing indispensable for the manufacture of white tubs had to be observed, such as the selection of a suitable concrete mix with low heat generation, special care in cleaning and pretreating the construction joints, in placing and compacting the concrete, and adequate curing.

3.5 Expansion elements

Slotted channels and cable ducts

After completion of the shells of the tunnel and ramp blocks, work could begin on placing the precast elements for slotted channels and cable ducts. For drainage of the road surface, slotted channels are arranged on the lower side of the transverse slope of the carriageway. These have a cross-section of 150 mm diameter and drain via inlet shafts with a baffle into the cast-iron collector pipe d = 300-400 mm located in the tunnel floor. In the area of the tunnel low points, where the natural slope of the tunnel floor was not sufficient for longitudinal drainage, slotted channels with their own slope were installed. The cables required for the tunnel equipment were laid in precast cable ducts. Where the cable duct and the slotted channel are on the same side of the carriageway, they are combined into one precast element. The precast elements have a standard length of 2.0 m.

Road structure

In the tunnel and ramp structures, a 70 cm thick road structure consisting of 36 cm crushed stone, 22 cm bituminous base course, 8 cm binder course and 4 cm chippings mastic was placed on the concrete base. Any small amounts of water that may pass through the pavement are fed through the ballast to a drainage pipe laid at the low point of the cross-slope on the tunnel floor.

Caps and noise protection measures

One of the last steps of the concrete construction was the production of the in-situ concrete caps in the ramp area and in the narrow tunnel structures of the access and exit ramps as well as the installation of the noise protection elements in the wall niches of the ramp blocks and the tunnel blocks in the portal area. The precast elements are 1.05 m wide and up to 6.5 m high. The cross-section consists of a base layer of 10 cm reinforced concrete and a profiled absorption layer of piled concrete. The precast elements are supported at the bottom in grouting pockets and held at the top by stainless steel angles and anchor channels.

After completion of the tunnel shell in 2001, the operational equipment of the tunnel was installed in parallel with the production of the lining elements. Prior to commissioning in 2002, an extensive safety exercise was carried out with the participation of the local safety services.

4. Literature

[1] Jacobi, Klaus und Sobotta, Joachim:

Die Flughafenbrücke- Die Rheinquerung

der Autobahn A 44 zwischen Düsseldorf und

dem linken Niederrhein

[2] Landesbetrieb Straßenbau NRW,

Niederlassung Krefeld:

Tunnel Strümp, Kurzdokumentation

[3] Landesbetrieb Straßenbau NRW,

Niederlassung Krefeld:

Tunnel Rheinschlinge, Kurzdokumentation

 

 

• Country: Germany
• Region: Nordrhein-Westfalen
• Tunnel utilization: Traffic
• Type of utilization: Road tunnel
• Client: Bundesrepublik Deutschland
• Consulting Engineer: Landschaftsverband Rheinland/lngenieurgemeinschaft A 44 Rheinquerung llverich
• Contractor: Dyckerhoff & Widmann AG, Walter Bau AG, Heilit + Woerner Bau AG, Ed. Züblin AG
• Main construction method: Open
• Type of excavation: Cut-and-cover
• No. of tubes: 1
• Tunnel total length: Rheinschlinge 870 m, Strümp 640 m
• Cross-section: each tubes: 3 lanes (each 3.50 m) plus hard shoulder (2.40 m)
• Contract Volume: 220 mill. DM (roughwork)
• Construction start/end: approx. 4 years
• Opening: 2002