Foundation laying in a sensitive environment, Stockholm, Sweden

Convenient, reliable casing advancing technology                    

Subject: Foundation laying in a sensitive environment

Location: Rosenlundsterassen, Stockholm

During the winter and spring of 2007, Hercules Grundläggning AB laid the foundation for a car park and seven-storey building next to the Skatteskrapan (“taxation skyscraper”) at Rosenlundsterassen in Stockholm. Since drilling was done at the same time as the building of the concrete wall for the Söderledstunneln (the Southern Route Tunnel), and since the adjacent ground is made up of old building spoil and boulders, it was very important not to introduce large amounts of air into the formation. If used here, air-powered technology might have caused movement and subsidence in the ground, which in turn might have damaged the tunnel wall and the surrounding buildings.

Hercules has used Wassara’s water-powered technology before, during drilling operations near the Swedish Parliament Building and the Malmö City Tunnel.

“The technology was convenient, reliable and efficient for casing advancing, so it was a natural choice to use the same method again,” says Rolf Karlsson, site manager at Hercules.

They drilled in two stages and used two different hammers to drive down RD piles. Stage 1 was excavation. First they dug through spoil, then 1.5 meters of broken rock, before reaching solid rock. Using a W120, a prototype version of the new casing advancing hammer, they drilled 45 holes between 3 and 6 meters deep alongside the concrete wall of the Southern Route Tunnel.

Stage 2 went through two existing parking decks. There they drilled around 60 holes with a W120 with depths from 3 to 24 meters. About 40 holes were also drilled with the proven W100 model.

According to Rolf Karlsson, both hammers worked very well.

“They performed like clockwork,” he says. “They’re the best we’ve used so far when it comes to drilling in ground where the surroundings mustn’t be disturbed.”