Norwegian civil engineering contractor HAB Construction is using six MP250 hydraulic struts from Groundforce Shorco to stabilise a deep excavation on the NK26bn (£2.2bn) Follo Line Project.
The Follo Line, where Norwegian National Railway Administration (Bane NOR) is the builder
is Norway’s new high-speed rail project connecting the capital, Oslo, with the town of Ski, approximately 25km to the east.
Most of the new line will be in a single tunnel, the longest railway tunnel in the Nordic countries, and much of HAB’s work involves deep excavations.
Groundforce was called in earlier this year to provide lateral support for an excavation that was showing signs of instability.
The six props comprise MP250 modular hydraulic units each with a maximum load capacity of 250 tonnes. Each of the props comprises a MP250 hydraulic unit, swivel assemblies to fix them to the capping beams and modular 1,016mm-diameter extension tubes plus tube adapters. They range in length from 20.5m to 25.8m.
Groundforce delivered the components on four wagons. The swivel plates and end bearing plates were pre-assembled, with load-monitoring pins installed in six of the assemblies so that loads on each of the six props can be monitored in real time following installation.
This is the first contract that Groundforce has carried out for HAB Construction and represents a further strengthening of the British company’s presence in the Scandinavian region. As well as other phases of the Follo Line project, recent contracts have included the massive “Barcode” project, also in Oslo, and the Valand Quarter near Gothenburg, Sweden.
The company’s activities in the Norwegian capital attracted the attention of HAB Construction, which contacted Groundforce as soon as it identified a need for swift structural support.
“Our props were in use just around the corner on a Keller phase says Sam Oldroyd. “There was an issue with the concrete wall that moved during the excavation of the foundation so we were called in to provide a remedial solution,” he adds.
The excavation is supported by conventional tubular steel beams at the surface – in accordance with the original design – with the Groundforce props installed as a remedial solution at the bottom following unexpected movement. The geometry of the excavation required each prop to be installed at a slight raking angle, braced between the concrete beam at one end and thrust blocks cast into the basement slab at the other. The beams are therefore inclined at angles of between 2.66o and 9.11o to the vertical.
The swivel assemblies, which are designed to adapt to horizontal deflections, were rotated through 90o to accommodate the vertical angles.
The Groundforce equipment was on hire for eight weeks.