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Wassara™ technology convenient and efficient in downtown Stockholm

During the winter and spring of 2007, Hercules Grundläggning AB laid the foundation for a car park and seven-story building next to the Skatteskrapan (“Tax Skyscraper”) at Rosenlundsterassen in Stockholm.

wassara technology

Since the drilling was being done parallel to the concrete wall for the Söderled Tunnel, and because the adjacent ground consists of old building spoil and boulders, it was very important not to introduce large amounts of air into the formation. Used here, air-powered technology might have caused ground movement and settling, which could have in turn damaged the tunnel wall and surrounding buildings.

Hercules had used Wassara’s water-powered technology before, when drilling near the Swedish Parliament Building and the Malmö City Tunnel.
“The technology was convenient, reliable and efficient for casing advancement, so it was only natural to use the same method again,” says Hercules site manager, Rolf Karlsson.

Hercules drilled in two stages, using two different hammers to drill RD piles. Stage 1 was the excavation process. First they dug through spoil, then through 1.5 meters of fractured rock before finally reaching solid rock. Using a W120, a prototype version of the new casing advancing hammer, they drilled 45 holes to depths of between 3 and 6 meters deep alongside the concrete wall of the Söderled Tunnel.

Stage 2 passed through two existing parking levels. There they used a W120 to drill some 60 holes, which varied in depth from 3 to 24 meters. About 40 holes were also drilled using the proven W100 model.

According to Rolf Karlsson, both hammers worked very well. “It went off like clockwork,” he says. “They’re the best we’ve used to date when it comes to drilling in ground where the surroundings cannot be disturbed.”


Hammer Wassara W100 and W120
Bit Symmetrix 139 x 10 and 168 x 10


Drilling fluid Clean water
Rig Soilmech
Formation Spoil on layers of broken rock
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