|
The difficult boundary conditions presented the site crew and formwork technicians with some tough challenges: The water table is only a very few metres beneath ground level, meaning that the building pits have to be waterproofed with sheet-pile walls and an underwater-concrete invert. As the tunnel structure will be entirely in groundwater after completion, the 67 concreting sections all have to be constructed in “waterproof tank” quality, with double joint-sealing tapes. The cramped site conditions make matters even more difficult: There is only 1.20 m of space left for the formwork – and for operating the formwork – between the outside wall of the tunnel and the sheet-pile wall. Because the back-stay anchoring of the sheet-pile walls protrudes into this clearance zone, lifting the outside formwork of the tunnel by crane was practically out of the question.
Instead, Doka Engineering planned and supplied a self-travelling “tunnel formwork machine” assembled from rentable system components. It consists of an all-hydraulic inside tunnel-formwork unit and an outside tunnel-formwork unit that can be repositioned with no need for a crane. The inside travelling tunnel-formwork unit is based on a framework made of SL-1 components, onto which fold-away elements of Top 50 large-area formwork have been fitted. Its 8 hydraulic cylinders and 2 hydraulic motors enable the forming operations to go ahead at the push of a button. Setting up and striking the two formwork-halves; lifting and lowering the tunnel-formwork unit and then travelling it on rails using flanged wheels – all this is done 100% hydraulically. The outside formwork can also be repositioned by the site crew in one piece, on roller blocks – again, with no need for a crane. For this, Doka designed the two formwork-halves as a telescopic three-hinged arch.
To save even more time, the Formwork Experts reinforced all the timber-beam formwork elements with Steel walings WU 16 and used 20 mm diameter form-ties. This has saved the crew 40 % of the wall-ties in each casting section. For 67 weekly cycles in all, that means at least 2500 fewer wall-ties! The manhours that would otherwise have gone into these wall-ties can now be used elsewhere. There is also less risk of water-permeable points on the structure.
Alpine Mayreder’s supervisor Kurt Knollmüller is very satisfied with how the forming operations have been proceeding. “An ingenious formwork system like this saves a lot of time on the site. And time, as we all know, is money!”
|
