Cost-effectively formed tunnel in Austria
Not far from the Dachsteingebirge Alps, the B145 - from the direction of Bad Ischl - connects the towns of Bad Aussee and Bad Mitterndorf with the B320 near Trautenfels. This provides a link from the southern Salzkammergut region to the A9 motorway A9 towards the city of Graz. Due to a number of avalanches in recent years, the 300-metre long avalanche protection gallery - built in 1994 - has had to be extended by a further 115 metres in a south-easterly direction.
For cost-effective construction of the nine concreting sections, each with 14-metre standard cycle lengths, the contractors are using a PERI formwork solution based on the VARIOKIT construction kit. Through the predominant use of standardized and rentable series production components, it has been possible to do without any special elements to a large extent. This has meant that the overall costs have been greatly reduced – particularly with regard to the small tunnel length and the short construction period.
Using the cut-and-cover method, the 12.80-metre wide arched cross-section has been designed for three lanes and is concreted above the bottom plate in a single operational sequence. The 60-centimetre thick tunnel arch extends along a 350-metre radius and features a 3.06 to 4.15 per cent lateral as well as 7.50 per cent of longitudinal gradient.
For this, PERI engineers created a formwork solution whereby the side formwork can be hydraulically swivelled inwards when striking as well as allowing the formwork carriage to be hydraulically lowered. In comparison to the conventional, manual striking process, this considerably eases working operations for the site personnel and also saves a great deal of time. Moving to the next concreting section is carried out on rails by means of electrically-operated chain hoists. The entire moving procedure only takes one hour – in spite of the large longitudinal gradient. The external formwork is moved from cycle to cycle with the crane.
For the experienced foreman, Martin Fladl from contractors Östu-Stettin, the easy and uncomplicated operability of the PERI formwork carriage is a tremendous advantage. Then, due to the hydraulic support during shuttering and striking, his formwork crew is extremely fast and able to maintain the tight construction schedule by achieving a 5-day cycle. Thus, two tunnel sections could be sometimes concreted in the space of one week with the VARIOKIT solution – a rather unusual occurrence in civil engineering.
Especially for individually planned engineering structures, the cost-effectiveness of formwork solutions can be clearly increased through the use of rentable system components. For the building contractor, this means smaller overall costs compared to using special solutions. Because the modular PERI VARIOKIT construction kit, with its standardised individual components, increases the utilisation rates of the independent parts and thus reduces on-site material requirements.
In addition, the VARIOKIT system from the Weissenhorn-based formwork and scaffolding specialists, PERI, offers planning engineers at the building contractors and engineering offices crucial advantages in the shoring and formwork planning: standardised connections simplify the planning process as well as static proof. Furthermore, during the actual construction phase, possible defective components can also be easily and quickly replaced.
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