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| VARIOKIT in tunnel construction  In order to relieve congestion problems in the centre of the Austrian town of Strasswalchen, a bypass is currently being built – the socalled west ring road. Certain parts of the bypass feature underground sections. PERI planned and supplied a 20 m long tunnel formwork carriage, complete with a hydraulic control system, which has played a key role in ensuring rapid realisation of the two tunnel tubes. Thanks to the new route, every day thousands of cars and trucks will be diverted around the town – a significant relief for the 7,000 inhabitants. As the Westbahn (Austrian Western Railway) as well as a stream cross the new route, a total of 955 m runs underground.The project was divided into two underground stretches of road with lengths of 688 m (underground stretch 1) and 267 m (underground stretch 2) respectively. The cross-sections of both tunnels are similar but have different wall heights and slab inclinations. The primary requirement of the contractor – HOCHTIEF Construction Austria – was constructing both routes with one tunnel formwork carriage which could be flexibly and easily adapted to suit all geometric changes. Furthermore, crane utilization should be kept to an absolute minimum whilst a drive-through possibility for construction site traffic was also to be provided. PERI design engineers planned a tunnel formwork carriage on the basis of VARIOKIT system components. The components of the engineering construction kit are designed for standard constructions with lengths of around 12 m to 15 m length; however, the Straßwalchen project requires a 20.60 m long tunnel formwork carriage. In order to realize this, two approx. 10 m long units were simply coupled together to create a project-specific tunnel formwork carriage. On completion, the construction crew will have used the carriage a total of 54 times: underground stretch 1 was realized in 36 concreting sections while 18 blocks have been planned for construction of underground stretch 2. The cross-section of both underground road sections varies in both width and height. The walls of the arched rectangular cross-section are between 55 cm and 75 cm thick, with height varying from 5.40 m to 6.50 m. Both tunnels have a clear standard width of 10.40 m although this increases to 14.00 m in the entrance of Underground Road Section 1 (casting segments 1 to 4). The change in the inclination of the bottom plate and tunnel slab requires a once-only modification of the transverse gradient of the formwork carriage; all other geometric adjustments are easy and quick to carry out before work commences on the following section. For adjusting the height of the wall formwork, PERI developed a practical solution: between the bottom vaulted formwork vertical wall formwork, a filler element is integrated so that geometric changes can take place without requiring any modifications to the vaulted formwork. This solution is extremely practicable as well as cost-effective. In the area of the widened tunnel cross-section, a PERI UP Rosett Flex scaffold construction supports the extended slab formwork, with the wall formwork simply being re-positioned on one side. The construction of the wall formwork with a waler line consisting of RCS rails is extremely rigid; consequently, a maximum of only three anchors is required for the complete height of the wall in order to connect the external and internal formwork. Thanks to this solution, the construction crew have been able to make considerable time-savings. For the stopend formwork, the client demanded a design solution whereby no bracing was necessary in those areas already concreted. PERI therefore created an inclined truss construction comprised of spindles and SRU walers which transfers the loads into the longitudinal beams of the formwork carriage and, from there, into the ground. In order to realize the required access portal, the formwork carriage is stiffened with VARIOKIT struts. HD 200 heavy-duty props carry the loads into the available strip foundations of the tunnel – thus, an additional support structure for the carriage is not required. Shuttering and striking of the internal formwork as well as raising and lowering of the slab formwork is done hydraulically. In addition, a moving unit has been integrated to ensure that the formwork units can be moved very quickly and conveniently to the next concreting section without the use of a crane. After this procedure, the two formwork carriages are re-coupled and prepared for construction of the next block. PERI design engineers also developed a project-specific, crane-independent solution for the external formwork: after positioning the internal formwork and installation of the reinforcement, the wall formwork elements are pulled forward on heavy-duty rollers in U-profiles by cable to the next casting segment. Already for the first, shortly completed tunnel blocks, the construction crew could concrete each section on a weekly basis thanks to the flexible and user-friendly design. Moreover, due to the high percentage of rentable system components, minimum use of a crane and the low number of anchors, the formwork solution is also very cost-effective. write your comments about the article :: © 2012 Construction News :: home page |