1. Task definition

The federal highways 93 and 175, as assigned federal highways to the federal highways A 4 and A 72, open up the economic area between Meerane, Glauchau and Zwickau. Due to the overlapping of through, destination and source traffic, both federal highways are heavily used, with destination and source traffic predominating by far on the B93 from Meerane to Zwickau. Considerations dating back to 1977 to widen the B 93 from Zwickau to the federal freeway A 4 to four lanes finally led in 1990 to concrete planning intentions for the construction of the federal road B 93 "Zwickau-Meerane". The decisive factor was the decision by VW Sachsen GmbH to build a new automobile plant in Mosel. The planning approval procedure initiated in October 1991 was concluded in February 1992 with the planning approval decision. 

Parallel to the planning approval, preparations were made for the invitation to tender for construction lot C, the most important and costly section of the overall project, with connection to the VW plant in Mosel. In this section, the route of the B 93 runs between the residential areas of the municipality of Mosel and the VW plant with a distance of only approx. 33 m to the residential buildings and the kindergarten. It also crosses the Zwickau-Dresden railroad line.

Due to the noise protection of the adjacent buildings and the crossing railroad line, the B93 between the new housing estate and the VW plant was planned in a tunnel, which is the most complex and most expensive structure of the entire B93 construction project.

Previously, the following variants had been examined in a noise protection report:

•  elevated road
•  Open trough
•  trough with noise protection covers (noise protection tunnel)
•  closed tunnel.

It was found that noise protection equivalent to the tunnel variants could not be achieved with an elevated road, even with extensive noise barriers. In addition, the low-lying sections proved to be more cost-effective.

The decision was made in favor of the closed tunnel for economic and urban planning reasons.

From a structural point of view, the closed cross-section offers more economical options for the transfer of lateral pressures (groundwater). From an urban planning point of view, the covered structure offers far greater design possibilities for terrain modeling and planting.

2 Design of the structure

2.1 Gradient and roadway cross-section

In the area of the Mosel tunnel, the route of the B93 runs in an arc R = 600 m, with a subsequent clothoid A250/200 and a subsequent counter-arc R = 500 m. In the elevation, the route is in the form of a curve. In the elevation, the route lies in a trough rounding with H = 500 m as a transition of opposite longitudinal gradients from 1.65 % to 4.5 %. The B 93 will be built with four lanes, with additional lanes for on and off ramps for each carriageway, so that 2 tunnel tubes with 3 lanes each were required. The road in the tunnel will be built with the same structure as on the open road, i.e. with

• 4 cm chippings asphalt mastic 0/11 S
• 8 cm binder course 0/22
• 18 cm bit. Base course C 0/32 CS
• i. M 76 cm frost protection layer.

The structure was placed on a concrete levelling layer B25 with a thickness of 8 - 28 cm, which supports the transverse slope of up to 4.5 % and is sealed on its upper side with welded sheeting in accordance with ZTV-BEL-B.

2.2 Cross-section and structure length

Each of the two tunnel tubes has a cross-section width of 3 x 3.50 +2x 1.00 +2 x 0.50 = 13.50 m. Based on the clear height of 4.50 m and at least 0.30 m clearance for accommodating the lighting, the clear structural height, taking into account up to 4.5% transverse gradients, is 6.32 m, which in section through the gradients is as follows:

• Clearance for lighting i. M.:0.58 m
• Clear profile height: 4.50m
• Pavement structure:0.12m
• Base course: 0,18m
• Frost protection layer: 0.76m
• Concrete leveling: 0,18m ... 6,32m

In three consecutive tunnel blocks, the clearance above the drive-through profile was increased by 0.60m to accommodate signage.

The transition blocks between the normal profile and the signage profile were designed with linear elevation changes. In three tunnel blocks, the tunnel cross-section was widened laterally to accommodate jet fans.

The length of the structure, including the two ramp troughs, results in

60 m (east ramp) + 428 m (tunnel) + 68 m (west ramp) = 556 m.

The carriageways in the tunnel are drained via slotted channels which are connected at intervals of approx. 40 m via manholes to the continuous longitudinal pipeline (DN 300) under the emergency walkway.

Due to the change in cross slope within the tunnel, the longitudinal drainage had to be distorted accordingly. At the tunnel low point, the surface waters are brought together in a collection shaft and fed via a transport pipe (DN 1000) into the pump chambers at the operating building 300 m away.

2.3 Ground and groundwater conditions

In the ramp areas, the bottom edge lies in Pleistocene gravel. Under the tunnel floor, there is predominantly Rotliegendes, so that a shallow foundation was possible throughout. Since the possibility of encountering stressed groundwater in the foundation level could not be ruled out, the design provided for the selective installation of filter layers.

At the encountered groundwater level, buoyancy safety was ensured by the weight of the structural concrete and the gradient-compensating concrete; the superstructure was not to be applied.

2.4 Design and construction

The tunnel was designed as a water-impermeable reinforced concrete structure in B25 with high frost and de-icing salt resistance and maximum permissible crack widths of 0.15 mm, and the cover was to be partially prestressed in the transverse direction with prestressing cables without bond. Construction joints were only permitted between the invert and walls in the control areas.

The three tunnel blocks under the rail crossing are sealed from the outside throughout with bitumen sealing sheets (3R 500 N) under protective or facing concrete. Reinforced neoprene waterstops are located in the section joints.

The design provided for a permanent groundwater drawdown of 2.50 m, resulting in the length of the ramps. For the construction of the entire structure in an open excavation, a further temporary lowering of the groundwater level had to be carried out. The excavation pit walls were secured with anchored diaphragm walls (d = 0.80 m). During the entire construction period, the excavation pit was to be shaded on the east side to prevent the inflow of water into the excavation pit.

The tunnel walls were to be concreted only with internal formwork against the diaphragm walls, with the possibility of sliding between the tunnel and the diaphragm wall being ensured by an insulating layer of rigid polystyrene covered with foil.

In the area of the railroad crossing, auxiliary bridges were required for the construction of the tunnel blocks under the railroad body. For safety reasons, a lateral working space was provided between the excavation support (diaphragm wall) and the tunnel structure, which subsequently had to be backfilled.

2.5 Tunnel equipment

The tunnel is equipped with operational facilities (lighting, CO measuring niches, jet fans and emergency call equipment). The corresponding lines are routed in DN 100 cable conduits, which run under the emergency walkways in a gravel bed and are led to transfer shafts at the tunnel portals.

3. Construction

Due to a secondary offer, the excavation pit shoring provided for in the design was not constructed as a diaphragm wall, but as a watertight sheet pile wall with a tie-in into the existing Rotliegende. In order to be able to vibrate the sheet pile sections (ARBEDKRUPP PU 20), overlapping boreholes 0 88 cm were drilled, which were filled with a bentonite-sand mixture in the lower 3 meters and with sand in the remaining area. Parallel to this, a transverse bulkhead of large bored piles was constructed at the interface with the railroad line. After the excavation support had been installed and anchored for 1/3 of the structure length in each case, the tunnel was constructed in its normal section starting from the railroad track in an easterly direction. The 39 sections, each 10 meters long, were concreted monolithically in weekly cycles using a formwork carriage without construction joints. In each section, approx. 900 m3 of B25 concrete, approx. 901 reinforcing steel bars and approx. 3 tons of prestressing steel were used for the bondless transverse prestressing of the carriageway slab.

In the area of the railroad crossing, the shoring for the three tunnel blocks was made of bored piles 0 88 cm, which also served as supports for the auxiliary bridges. The tunnel blocks under the railroad were shuttered conventionally.

The tunnel ramps were advanced with a time delay parallel to the work on the tunnel.

The finishing work followed 7 months later with the placement of the profiled concrete, its sealing and the laying of the empty pipes, curbs and drainage systems.

During the construction period, it became apparent that permanent groundwater subsidence was avoidable. Therefore, the ramps were redesigned compared to the design. They were extended and raised above the groundwater level. This results in an east ramp length of 122 m (instead of 60 m) and a west ramp length of 150 m (instead of 68 m), i.e. a total structure length of 700 m. For buoyancy control, reinforced concrete bored piles 0 130 cm were installed in the west ramp along the runway, which are firmly connected to the base slab. In each of the ramp areas, one pump shaft proved to be sufficient for open dewatering.

In the tunnel area, the day water was led during the construction period to a collection shaft at the lowest point of the route and from there pumped into a settling basin.

To achieve a concrete that was as crack-free as possible, the cement content of 317 kg/m3 PZ 35 F was topped up with 60 kg/m3 of hard coal fly ash at a WZ = 0.5.

As a concrete curing measure, the formwork carriage remained in position for 5 days after concreting to prevent excessive heat dissipation. The concreted section was also suspended with sheeting to prevent drafts.

Insulated external formwork was used on the outer walls, and the tunnel ceiling was covered with thermal insulation foil.

In three tunnel sections, control measurements of the concrete temperature were taken via heat sensors during extreme outside temperatures in order to be able to control the curing (if necessary, interior heating).

The tunnel, which was constructed as a "white tank" without external sealing, was covered with soil and provided with a pleasing planting of native trees and shrubs.

4. Literature

[1] Straßenbauamt Zwickau: „Neubau der B93 Zwickau - Mosel - Meerane" (Prospekt)

[2] Max Bögl Bauunternehmung: „Neubau der B93 Zwickau - Meerane" (Sonderprospekt)

 

• Region: Freistaat Sachsen
• Tunnel use: Road
• Client: Freistaat Sachsen repr. by Straßenbauamt Zwickau
• Consultants: Zierl Consult, Huber u. Partner, BUNG Ingenieure
• Contractors: Max Bögl GmbH, Dürr GmbH
• Tubes: 1
• Total length: 122 m + 428 m + 150 m
• Cross-Section: 2 x 93m²
• Contract value: 59 Mio. DM (Rohbau), 6 Mio. DM (BTA)
• Contruction time: 07/1992 bis 12/1993 (17 Monate)