WATER-POWERED DRILLING INSIDE STOCKHOLM S CENTRAL STATION

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1 WATER-POWERED DRILLING INSIDE STOCKHOLM S CENTRAL STATION FOUNDATION REINFORCEMENT PROJECT Water-Powered Drilling inside Stockholm s Central station LKAB Wassara, All rights reserved.

2 WATER-POWERED DRILLING INSIDE STOCKHOLM S CENTRAL STATION LKAB Wassara AB, Stockholm, Sweden (Photo courtesy of Jernhusen) The Stockholm Central station has been sinking 1 mm per year and needed reinforcement of the foundation. This was done by drilling and setting casing all the way down to the bedrock. Niches were cut out from the side of the existing foundation walls, big enough to allow access for a small drill rig. Wassaras water-powered DTH hammer was prescribed for the project as the environment was sensitive in several ways. STOCKHOLM CENTRAL WAS A SINKING STATION The Central station in Stockholm is the very central point in the Swedish railway system. 80% of all domestic journeys by train starts or ends here. An average of commuters pass here every day. The station was completed in 1871, with some parts built on what used to be a lake. Before building the station, parts of the lake was filled with sand, gravel and boulders. Numerous oak pillars serves as foundation, but later on it became clear that the pillars don t reach the bedrock. Measurements indicated that the main station building was sinking more than 1 mm per year. FOUNDATION REINFORCEMENT The landlord Jernhusen hired the construction and project management company Forsenprojekt for the reinforcement project. The contractor Lemminkäinen was awarded the contract for the later part of the foundation works. This part of the project included the installation of 428 steel piles, placed every second meter in the foundation wall and down into the bedrock. The sensitive environment demanded as benign drilling as possible. No noisy machinery or dust in the air was allowed. Any vibrations must be kept at a minimum. The water-powered drilling with Wassara is the only percussion drilling technology that meets these demands. A PROJECT WITH MANY PARTICULAR DEMANDS As parts of the building are listed as a National Heritage, strict national laws applies; the building must not be damaged. The available workspace for the operation was quite cramped, due to bulky foundation walls. To further complicate the works, multiple parallel construction projects were running at the same time. As the public area was in full operation, some commuters were passing very close to the drill site every day. This pushed the environmental aspects with low noise even further. It also made the moving of drill rigs and other machinery limited to off-peak hours. DRILLING INSIDE THE FOUNDATION WALLS Niches were cut out from the side of the foundation walls, big enough to allow access for a small drill rig. The drilling and casing advancing was done all the way down to the bedrock, an average of 16 meters. LKAB Wassara AB info.wassara@lkab.com (5)

3 Water-Powered Drilling inside Stockholm s Central station The formation was full of oak logs that had to be drilled through. After the casing was set, arrangements were made in the walls to enable the support of the new pillars. This was repeated every second meter of the wall. CREATING NEW SPACE The Central station s lower hall accommodates several stores and small shops. In order to create more space, the number of the rather bulky foundation walls needed to be minimized in this area. Some m 2 of new area has been created in the lower hall. This was achieved by excavation of new areas and lowering of the floor level, as well as replacing bulky walls with supporting steel pillars. PLEASED CONTRACTOR Oskar Nilsson at Lemminkäinen was Site Manager during the reinforcement project. - The drilling went as planned, he says. When drilling indoors, we arranged for the return water to be collected and pumped away. The oak logs didn t cause too much of a problem. Our biggest challenge was the logistics; working so close to the commuters that walked by every day as it demanded special arrangements for our machinery and hoses. Drilling and casing advancing inside a niche PROJECT TIME January 2010 March 2013 Equipment used DTH hammer Wassara W80 Wassara W100 Wassara W120 The new pillars (in the bottom) are now supporting the foundation. The niche is ready to be closed and filled with concrete. Drilled RD-piles Wassara W150 Ruukki RD90, RD 115, RD140, RD170 & RD220 The W80 hammer Rig Geomachine Kelpo S Pump Drilling fluid Lemminkäinen HP500/180 Clean water The W100 hammer Drill pipe 76, 89, 102 and 140 mm Borehole length Scope of drilling Geologic formation meters meters Sand, gravel and boulders, together with oak logs The W120 hammer The W150 hammer LKAB Wassara AB info.wassara@lkab.com (5)

4 Water-Powered Drilling inside Stockholm s Central station RIG ON THE MOVE The moving of the rig was often limited to off-peak hours when working close to public areas. SETTING UP FOR THE NEXT BOREHOLE Aligning for the next casing, indoors under the Central Station. The tight spaces made the alignment of the drill rig complicated. DRILLING IN CRAMPED WORKSPACES The drilling went as planned, despite the cramped workspace in the niches. The welding of the casing pipes presented another challenge. THE WALLS As the foundation with oak pillars don t reach the bedrock, the walls were sinking 1 mm per year. (Illustration courtesy of Lemminkäinen) REINFORCEMENT WORKS The drilling and casing advancing was done all the way down to the bedrock, up to 24 meters. (Illustration courtesy of Lemminkäinen) MANAGING THE WATER The incoming water came from municipality sources. Arrangements were made for the return water to be collected and pumped away. LKAB Wassara AB info.wassara@lkab.com (5)

5 WASSARA COST-EFFICIENT AND ENVIRONMENTALLY FRIENDLY DRILLING LKAB Wassara is a Swedish company developing and manufacturing unique waterpowered drilling systems for high performance in surface- as well as underground drilling operations. The heart of the Wassara drilling system is the world patented water-powered down-the-hole hammer. The drilling systems have been used for more than 20 years in various applications within many industries; mining, exploration, ground engineering, dams, geothermal, marine, oil & gas storage. Our experience covers more than 25 million drilled metres working in different locations around the world. Reference studies can be found on our website. LKAB Wassara was founded in 1988 and is owned by LKAB. LKAB is an international high-tech minerals group that produces iron ore products for the steel industry and other mineral products for many other industries and applications. Explore more at LKAB Wassara AB info.wassara@lkab.com