Back in 1981, the French railway company SNCF was the first company to start high-speed train service in Europe. Since then, the SNCF has constantly expanded its high speed train network. In late 2011, its new Rhine-Rhone high speed line will start operation and drastically cut down travel time from the Alsace, South West Germany and Northern Switzerland to Paris, Lyons and the Mediterranean. Part of the new line is an inner-city rail link in Mulhouse. Contractor Maïa Sonnier S.A. used different MEVA formwork systems and solutions to efficiently handle the various forming challenges when building the tunnel and bridges required for the inner-city rail link in populated area.
Tunnel walls poured with heavy-duty wall formwork
The aboveground tunnel integrates the rail link into the propulated area without dividing it into two parts. It is 122 m long and has a clear width of 5.5 m. Its walls were poured with MEVA’s heavy-duty wall formwork system Mammut 350 that handles fresh concrete pressures up to 100 kN/m² so that walls up to 4 m can be poured at any speed without considering the fresh concrete pressure. This benefit saved much working time when pouring the 6.50 m high walls in 10 m cycles. Large-format Mammut 350 panels were ganged horizontally and height-extended to achieve formwork units 10.5 m long. Four units were used per cycle, one outside and one inside at either wall.
Formwork transport by winch saves 15 working days
The two outside formwork units had working platforms, walkway bracket, access hatches and ladders. Each time a cycle was finished, the outside formwork was disassembled into large parts and the parts crane-lifted to the next cycle. The inside formwork units were equipped with support frames STB 450 and trolley walers. These mobile units were pulled with a winch to the next cycle. Pulling entire units to the next cycle saved 1.5 working days per cycle, i.e. 15 working days for the tunnel. A new cycle could be poured every 3.5 days rather than every 5 days.
Bent, rising and with curved Portals
The track in the tunnel makes a slight curve. Yet the tunnel walls are not consistently curved but polygonal. At the end of each cycle the formwork for the next cycle was placed at an angle of 2° to the poured wall of the last cycle to achieve the polygonal tunnel form. In addition, the track rises with a grade of 7.5 ‰ but the concrete joints were to be vertical. This challenge was handled by positioning the large formwork units completely horizontally on the ground and using timber wedges between the ground and the panels. The tunnel portals on both ends are shaped like the aerodynamic power head of the French TGV high speed train. After all other wall cycles had been poured, the 10.5 m long wall partitions with the portals on both ends were poured using the Mammut 350 panels of the outside formwork units that were no longer needed. The curved portals were formed with special wooden formwork supplied by a local company.
Table forms on mobile MEP shoring towers save time
The tunnel slab, 50 cm thick and with a 20 cm concrete haunch on both sides, was constructed with table forms on H20 girders that rested on MEP shoring towers. Four tables with a total forming area of 60 m² were used per cycle. Each table rested on three MEP shoring towers which were connected with scaffold tubes to form one single unit. The shoring units including H20 girders and table forms were moved from one cycle to the next using transport walers and winches. There was no need need to disassemble and reassemble the units, and this saved considerable time. The edges of the tunnel slab were poured using the hand-set EcoAs formwork and the working scaffold KAB 190 to work on.
Piers and foundations of the foreshore bridges
The railway track passes the Rhine-Rhone canal on a frame bridge. The long ramp before the frame bridge and the short ramp between the frame bridge and the tunnel were constructed as foreshore bridges that fit well into the surrounding area. The pier foundations were formed with the Mammut 350. Each pier has a rectangular middle part with negative imprints (achieved with wooden slats on the facing) and a prefab concrete half-shell on either side. As the foreshore bridges descend on either side of the frame bridge, the piers’ rectangular middle parts have different heights. They were formed with plywood facing, the highest piers first. Then the plywood facing was cut down to the size of the lower piers. Thus, the same facing could be used for all piers of different heights.
Four abutments and their foundations were constructed with the Mammut 350. The foundations for the two abutments at the beginning of either foreshore bridge measure 6 x 6 m and 5 x 5 m. The abutment walls are up to 3.20 m high. A bigger forming challenge were the two abutments that connect the frame bridge with the foreshore bridges. Both are elongate and bent approximately in the middle, with an offset on the outside. The abutment walls, 1.30 m thick and up to 4.35 m high, were formed with the Mammut 350. Its articulated corners were used to form the bend on the inside of each abutment. Wooden fillers and formwork parts were used for the offset on the outside. The entire formwork was planned and set up in a way it could be used for both abutments, with only minor modifications necessary for the articulated corners and wooden parts.
Biggest challenge: The frame bridge over the canal
The frame bridge with its 20 m span was the biggest formwork challenge of the entire project. No bridge piers could be erected in the canal bed because they would have impeded shipping traffic. So the only solution was constructing the bridge in the form of a wide and long rectangle covering the entire width of the canal and resting on a row of columns on either side of the canal. The track runs diagonally over the bridge. The colums are 1.60 x 1.30 m and 1.30 x 1.30 m wide and long, with a centre-to-centre distance of 3 m. They were formed with the Mammut 350.
Load: 25 tons per running meter
Each column row supports a concrete beam that is 1.50 m high and up to 2.10 m wide. Both beams were poured with the Mammut 350 and carry the concrete parts that make up the bridge superstructure. These concrete parts – each weighs 40 tons – were poured on site, then placed with a crane onto the bridge beams and supported by MEP HD (heavy duty) props. Three props per running meter were placed on the sheet piling on either side of the canal bed to transfer 25 tons of load per running meter. Special steel profiles at the top and bottom of the props allowed for a smooth and consistent load transfer.
Close cooperation between contractor and MEVA
The project’s formwork detailing including structural design was done by MEVA France in close cooperation with the site management of Maïa Sonnier. Thanks to the excellent cooperation and on-site support by MEVA’s Alsace office all work was done efficiently and terminated on time
Follow-up project: Parking deck
The number of train passengers will rise significantly when the high-speed line starts operation in December 2011. Many train passengers will arrive by car at the Mulhouse station. That is why a large parking deck is being built there. It will offer parking for 450 cars and MEVA’s slab formwork system MevaDec is used to pour the parking deck’s slabs.
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The solution: table forms, 5.40 m long to exactly fit into the openings between the columns. Short filler pieces with rounded edges provided a perfect match to the column layout.