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Cost-effective realisation of arched tunnel for safe animal crossing
Wild game underpass RN 88 near Albi-Rodez, France
The RN 88 highway connects Lyon and Toulouse and this route is currently being expanded to four lanes in some areas. Between the towns of Rodez and Albi in the south west of the country, a wild animal underpass is being constructed near a nature reserve. In order that the animals do not shy away from using the tunnel, a very generous cross-section was planned for the 80 m long structure. A small stream also runs along the complete length of the 15.00 m wide and 9.24 m high, semi-circular tube which is being constructed above the bottom plate as a single unit using a cut-and-cover method.
Formwork carriage from rentable VARIOKIT system components
For constructing the arched cross-section with a 50 cm wall thickness, PERI engineers in Meaux, near Paris, planned a solution based on the VARIOKIT engineering construction kit. The main components of the 10 m long formwork carriage are SRU steel walers, HDT main beams and SLS heavy-duty spindles. For the transfer of loads in the strip foundations, HD 200 heavy-duty props are used. The extensive utilisation of system components significantly increases the cost-effectiveness of the formwork solution: alongside of the serial components were only a few purchased parts (couplings, timber formers) and consumable materials such as the formlining.
PERI supplied pre-assembled formwork elements and platforms with up to 2.50 m widths on a just-in-time basis to the jobsite. A supervisor supported the construction team during the final assembly of the formwork carriage directly on site.
Mechanical solution - easy handling
Due to the low number of uses of the formwork carriage, it was decided not to use hydraulic components for shuttering and striking or moving procedures. The main focus during the planning of the mechanical solution was on the ease of use.
For shuttering and striking, the construction team utilises simple spindles. In order to pivot the side elements inwards, only the lowest spindle has to be used. By releasing the heavy-duty wedges under the HDT girders, the entire formwork unit is lowered by around 8 cm. In the subsequent casting segments, the formwork carriage is pulled by means of two winches with the flat and straight course of the tunnel simplifying this process.
Hydraulic jacks bring the formwork carriage into concreting position after moving, the side elements are then spindled upwards. Extensive prefabrication of the reinforcement sections directly next to the tube accelerates their installation. Finally, a mobile crane moves the external formwork into position which consists of only two elements per side. For placing the concrete, 12 concreting windows are used whilst compaction is carried out through internal vibrators.
Through the simple mechanical operations of the formwork carriage, the construction team was able to achieve a four-day cycle per concreting section after a very short familiarization period.
A completely safe solution
Apart from the easy usability of the formwork carriage, the safety of site personnel has the highest priority. Among other things, the carriage has generously-sized working levels that are pre-assembled on the external formwork. SRU steel walers and GT 24 lattice girders form the sub-structure of the platforms. The construction site team is guaranteed secure working conditions through the 1.10 m high PROKIT side mesh barrier which is fitted to all open edges.
The PROKIT system components allow open building edges to be reliably secured whilst requiring little installation effort. Only three system components are used - side mesh barrier, post and slab foot. The slab feet are screwed onto the wooden planking and accommodate the posts. These are self-locking and, as a result, can quickly and safely installed. Subsequently, it is an easy task to attach the 2.40 m long, powder-coated mesh barriers. PROKIT EP 110 can be used very flexibly due to a wide range of fixing possibilities on walls and slabs as well as being suitable for use on nearly all PERI formwork and scaffolding systems. Through the high utilisation rate of the individual components, the investment pays for itself in the shortest possible time.
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