Groundforce hydraulic propping equipment is once again helping to streamline construction of a large basement on Olso’s ambitious “Fjord City” project.
Specialist groundworks contractor Kynningsrud Fundamentering is using 16 of Groundforce’s MP250 to support a sheet-piled retaining wall which runs alongside 2 busy road next to the site.
The B3/B7 Project is part of the Bispevika portion of the Fjord City redevelopment in the Norwegian capital. Kynningsrud has been using Groundforce equipment to stabilise excavations since it started on the Barcode B13 contract in 2012-2013.
Kynningsrud also used the equipment during on this site which involved the delicate unearthing of a 15th Century ship that had been covered over centuries ago during land reclamation works.
Now Kynningsrud is now using the equipment on the B3 scheme and an adjacent site, B7. Together these site comprise a large L-shaped basement excavation.
All the Bispevika developments are located on reclaimed land that was underwater until the mid-19th Century. The ground is very poor and solid propping is absolutely essential.
This is especially true of B3, which runs adjacent to a main road. “It’s supported by huge numbers of piles and we can’t risk any movement.” comments Sam Oldroyd, Europe sales manager for Groundforce.
The method chosen by Kynningsrud involved excavating from the middle of the site outwards. First the central portion was excavated to formation level with the sides battered to a shallow slope to avoid collapse.
The central portion of the basement slab was then cast. The lateral forces from the sheet piled retaining wall which had been installed around the perimeter of the site could then be transferred to this portion of slab by a series of 21m-long Groundforce MP250 props installed as raking struts.
But these struts have to span the outer, unexcavated, portion of the basement lying between the central section and the retaining wall.
To enable them to do this, Kynningsrud has to cut them into the earth so they can be fixed to the waling beam at one end and to concrete thrust blocks cast into the slab at the other.
With the retaining wall thus supported, Kynningsrud then carefully removes the rest of the earth from around the struts, installing additional struts to support the lower level as the soil is removed.
The retaining wall is then fully supported and the rest of the basement slab can be cast.
“This type of procedure is actually quite commonplace here in Oslo because of the poor soil,” explains Sam. “But the difference here is that Kynninsgrud is using our hydraulic props which are very quick and easy to install and remove.”
This speed of deployment allows the contractor to ‘piggy-back’ the props as the excavation progresses along the line of the retaining wall, removing one prop when no longer required, and reinstalling it further along. Instead of propping the entire excavation in one go, Kynningsrud has required only 16 MP250s, which are spaced at 5m centres.
“The contractor’s managing to install up to six props in one day (12 h) and to remove and re-install four or five props in one day, which is phenomenal,” comments Sam. “Not only does this save money, because fewer props are required, it also saves on lorry movements to and from the site.”
Groundforce is currently active on several contracts in Scandinavia, where its modular hydraulic propping methods are quickly catching on.
Not only are contractors beginning to appreciate the technology, but Groundforce can supply equipment at very short notice from its depot in Hanover, northern Germany.