Winter, 1000 metres above sea level, 3 % longitudinal gradient, partly round and partly angular in section. The widening of the Stalvedro Tunnel in the Swiss Alps is a challenge. So on this build, (virtually) the entire range of Doka tunnel formwork systems ensures speedy, economical and safe progress.
320 metres long, the motorway tunnel in Canton Ticino was widened from two to three lanes, and the job had to be done within only a few short months. The first two lanes remained open to traffic, which meant that construction material had to be available quickly. Space was very much at a premium, so the structure had to be slim. And on top of all that the two tunnel portals are different shapes: the southern portal is round, its counterpart to the north is angular.
Faced with these varying challenges, the contracting consortium opted to use different tunnel forming systems. 240 metres of the tunnel were excavated by mining, 80 metres were cut-and-cover.
For the mined tunnel Doka supplied a special construction: a reinforcing carriage measuring 12 metres in length. It is followed by a steel forming carriage built by cooperation partner CPT for casting the tunnel vault. Then come three post-casting travellers (30 metres for provision of site materials), also special constructions, for the post-casting finishing of the tunnel's inner shell. Each carriage consists of a movable heavy-duty supporting system built from Top 100 tec components and a supporting structure of walings and scaffold tubes. Even though they were designed specifically for this tunnelling job, the special constructions consisted of 95% rental material.
The broadest DokaCC formwork traveller anywhere in the world was used for the tunnel's round southern portal, which is almost 15 metres wide. The tunnel's longitudinal gradient between the northern and southern parts runs at 3 %. This did not pose a problem, because the tunnel systems have electric drive motors and four hydraulic cylinders to raise and lower the carriages.