The challenges began with the delivery of the 115-tonne Liebherr LB 36 rig that was needed for the installaton of piles. A small harbour had to be specially built on the River Aare in order to assemble the machine. From there, the drilling machine was transported upriver. After days of rain, the high water level made the plan to manoeuvre the LB 36 under the bridge even more difficult. When the rig first passed through, there was a gap of just 500mm to 600mm between the leader and the underside of the bridge.
“This is a very special water construction site,” said Daniel Kunz, director of the contractor Birchmeier Spezialtiefbau. “We are operating with our drilling rig on a pontoon.”
The renovation of the 130-year-old bridge includes the strengthening of four piers, each involving the installation of four piles surrounded by a sheet pile wall. Using the Kelly drilling method, Birchmeier is boring the 16 piles with the LB 36. Each pile has a diameter of 1.5m and is between 12m and 20m deep.
Originally, it was planned that Birchmeier would reinforce the piers in winter, when less water flows in the Aare. However, this is when work must be stopped for a closed season for the fish.
After the hole has been drilled and the reinforcement cages have been inserted, the next challenge is to transport the concrete to the borehole. This has involved laying 280m of concrete lines to enable delivery using a Liebherr pump of type THS 110 D-K.