Tunnel concreting / Shotcrete
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A slab track system is being created in the Malmö city tunnel
A slab track is being laid in the tunnel section with two individual 6 km tunnels. The sleepers are embedded in concrete and can absorb the vibration caused by high-speed trains in a better way due to having an extremely flexible insert.
Maximum precision is required when the tracks are installed. The sleeper shoes that have been freshly embedded in the concrete must not be subjected to vibration. Even the slightest variations in the alignment of the tracks can result in the railway no longer complying with the original designs for high-speed travel.
The order for constructing the slab track in the Malmö city tunnel was placed with Rhomberg Bahntechnik GmbH. The objective was to find a solution for installing the concrete track bed over a distance of two times six kilometres without a major amount of vibration. The plan was to do the concreting at a speed of 15 – 20 m/h.
Railway engineering specialist Rhomberg (based in Bregenz in the Austrian Vorarlberg area) made contact with the representative of Austrian company Putzmeister, Hans Eibinger GmbH. Together with the Concrete Project Division department at the main Putzmeister plant in Aichtal, all of the parties involved collaborated to produce a solution for supplying a tunnel concreting train based on the patented installation solutions of Rhomberg Bahntechnik.
| Comprehensive planning
During the planning of the tunnel concreting train it had to be taken into consideration that the freshly embedded sleeper shoes could only bear a certain amount of load. Beginning with the setting speed of the concrete and the travel speed of the concreting train, it was calculated that a distance of between 250 and 400 m had to be maintained between the concrete paving machine and the pump unit. The entire pipeline would therefore have to be made mobile. The pump unit consists of an electrically powered concrete pump and two mixing drums, whereby the first one would be used to supply the system with fresh concrete, and the second one would provide the concrete for ensuring that a continuous concreting cycle could be maintained.
The concreting train consists of various railway wagons on which all of the necessary components for carrying out a continuous and smooth procedure are mounted (including the necessary cleaning and maintenance work). All systems are protected by an emergency power unit.
Pump and delivery line
The Putzmeister stationary concrete pump is on the third wagon, plus a small conveyor belt for feeding the concrete pump. In order to prevent the pump from drifting during the pumping procedure, the frame of the rail car is filled with concrete and the support legs of the pump are directly screwed to it. The pump can be operated using a cable-connected remote control during the pumping process. The concrete is transported from the pump to the concrete paver up to 400 m away via a steel delivery line that is installed on special wagons. The maximum permitted concrete pressure of the delivery line is 130 bar. The delivery line has a diameter of 125 mm and a wall thickness of 7.1 mm. Since the slab track in the Malmö city tunnel also has a long curve with a radius of 760 m, the line has been adapted accordingly in order to be able to run on the patented alignment system made by Rhomberg Bahntechnik. Non-critical load transmission was a challenge during dimensioning.
The patented paving machine is located at the end of the delivery line and consists of an upstream working and transport platform and a hopper. The concrete is transported to the track bed via three special chutes. The concrete is pre-smoothed using skimming boxes and then compressed using vibrators.
Particular attention was also paid to having an environmentally friendly disposal and cleaning concept that meets the strict regulations in Sweden. In order to clean the delivery line with water, a media separating device must first be installed. This ensures that residual concrete and washing water do not mix. The residual concrete in the line can therefore still be laid in the track bed. The media separation system consists of the combination of sponge ball – soaked cement bags – sponge ball – wash-out pig – sponge ball.
It was possible to successfully deal with this complex project by means of close collaboration between participating project partners Rhomberg, Eibinger and Putzmeister. Not least the competent service engineers from Eibinger and their involvement, along with the efficient service contributed to the success of this new solution for supplying concrete.
References Tunnel concreting