Project: Galgenbuck tunnel, Neuhausen/Schaffhausen, Switzerland
Builder: ASTRA ((Federal Swiss Road Department)
Contractors: Marti Bauunternehmung AG, Zurich, and STUTZ AG, Frauenfeld
Engineering and support: MEVA Formwork Systems, Seon, Switzerland
The Swiss village Neuhausen near Schaffhausen is famous for the Rhine Falls and will be relieved from heavy through-traffic by a 1,100 m long bypass which includes a tunnel. Contractor Marti Bauunternehmen AG, one of Switzerland‘s major contractors, is using the Mammut 350 wall formwork and STB 450 support frames to pour the retaining walls and bridge piers for the new road that connects the tunnel with the existing main road.
The building site is located at the bottom of a steep. Thick double retaining walls up to 16 m high need to be poured to contain the steep and keep the soil from moving. As if to complicate matters, the new connecting road is slightly curved and ascending from the main road to the tunnel, i.e. the formwork for the base slabs and wall sections has to be curved and set up at a different heights for each pouring cycle. What’s more, governmental safety regulations are very strict. So are the building authorities’ specifications with regard to quality and architectural concrete surface.
Thorough planning is a must because each cycle is unique
The size, dimensions, form and thickness of the base slabs and wall sections vary by cycle. A different formwork setup profile had to be created for each of the 25 cycles. The wall sections of all cycles, each approx. 5 m wide, were poured using three ganged panels, two of them 2.50 m wide and one varying in width.
Varying polygonal base slabs
The base slabs, also approx. 5 m wide and up to 9.78 m deep, grow thicker towards the hillside, achieving thicknesses of up to 1.80 m. The surface of the base slabs below and between the retaining walls is horizontal, outside this area it slightly descends towards the valley and hillside.
Double retaining walls
The enormous pressure resulting from the steep can only be contained by two parallel retaining walls. Depending on their location, the wall sections are 71 cm to 1,68 m thick at the bottom. For statical reasons, the valley side and hillside retaining wall sections differ in height.
The visible parts of the wall sections are tapering towards the top and, depeding on the wall section, one or both sides are inclined. This forming requirement was easy to meet by simply inclining the Mammut 350 panels. Thanks to the articulated flange nuts, tieing is no problem with inclined panels.
Architectural concrete with a board pattern
The visible parts of the retaining walls come with an architectural concrete surface and a board pattern which is achieved by attaching a plywood facing to the panels.
Ascending and curved
All retaining walls are poured on inclined ground requiring a vertical offset of the formwork setup cycle by cycle. Depending on the radius, the curved wall sections are achieved by either setting up the panels in a polygonal form or by curving and rounding out the plywood facing attached to the panels.
“We‘re making good progress,“ says site manager Tino Otten. „We opted for the Mammut 350 because it is strong and handles tough loads true to form – and that‘s an absolute must on this site.“
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