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Ruukki RD Drilled Pile Walls Enable Construction of Trondheim Tunnel

01/18/2011 - A retaining wall solution installed by drilling developed by Ruukki is enabling construction of a section of the Trondheim road tunnel in Norway, since vibration or other stresses that disturb the soil must be minimized.

A retaining wall solution installed by drilling developed by Ruukki is enabling construction of the Trondheim road tunnel in Norway, which is part of the E6 road project. The site conditions for the project are extremely challenging, since hardly any vibration or other stresses that disturb the soil are allowed.
 
Ruukki RD pile walls can be installed in extremely difficult conditions unsuitable for traditional retaining walls. It offers the unprecedented advantage of not requiring a separate construction-period retaining wall, since the RD pile wall can serve both as a temporary and a permanent structure. This is made possible by the foundation of the wall with RD piles of high load-bearing capacity. Use of the RD pile wall also allows accurate forecasting of total solution costs and installation schedule.
 
The RD pile wall is based on RD steel pipe piles, interlocks welded onto them at the mill and an installation method that uses reamer bits larger than normal diameter. The dimensions of the reamer bit and the interlocks allow drilling the RD piles through stones and boulders into bedrock without the interlocks getting stuck in soil, stones, boulders or the bedrock surface. In other words, the reamer bit cuts a hole larger than the outside diameter of the pile in order to allow the interlocks on the outer surface of the pile to fit into the drilled hole.
 
The RD pile wall is suited for applications involving vibration-sensitive structures as its installation causes less vibration than the installation of a sheet pile wall. When piles are driven through soil, down to bedrock, the structure can also function as a wall that resists earth loads, and as a foundation structure that transmits vertical loads e.g. in the underground sections of apartment blocks or office buildings.
 
The Ruukki solution was chosen in Trondheim because the site’s soil comprises very easily disturbed quick clay. Because the retaining wall must be installed with minimum stress to the soil, all the way down to bedrock, Ruukki’s retaining wall is one of the only possible means of building this section of the tunnel.
 
The Trondheim road tunnel will have a total length of 500 meters, 120 meters of which will be furnished with drilled pile walls. The tunnel is along the motorway section of the E6 road to be built between Trondheim and Stjordal.