RD® pile wall as support structure for excavation of polluted ground

Aarsleff used a brand new RTG RM20, Eco Mode piling machine for this project with a DTH system where the drill bit was mounted directly onto the pipe (Photo: Sondre Smeland – SSAB).

Golder Associates Norway (now a WSP company) and Per Aarsleff AS were involved with the survey process and the installation of the support structures. This was one of Aarsleff’s first projects in Norway using SSAB’s pile products. A total of 185 tonnes of RD piles with interlocks were drilled to 17 m depth and up to 7m into the bedrock. The wall was supported by internal steel beams and anchors drilled into rock and grouted to the bedrock. The RD pile wall structure covered an area of 594 m2. This structure has a resistance capacity of 951 kNm/m and 4288 kN in vertical capacity. RTG RM20, Eco Mode was used during the installation. This is a machine suitable for 18 m piles and drilling force of 201 kW giving 2000 rpm and allowing torque up to 120 kNm.

Exact Geo Survey AS performed settlement measurements during the installation phase to ensure the structural integrity of the surrounding buildings. Drilling of support structure has shown clearly reduced disturbance of neighbouring structures compared to ramming. If sensitive clay is also present, drilling is a gentler installation method. A water-based drilling system reduces impact on the nearby soil more compared to an air-based drilling system.

RD600/10 with RM/RF interlocks with bitumen (photo: Sondre Smeland – SSAB

The piles used in this project were manufactured at SSAB’s tube mill in Oulainen, Finland. Coils are delivered to Oulainen from SSAB’s steel mill in Raahe, Finland. 1060 m of RD600/10 S355J2H with bitumen-sealed RM/RF interlocks were transported by 7 trucks from Savikko Oy in 6 and 15 m lengths over 1800 km (one way). 140 m of RD400/10 S355J2H were also used as support structure alongside the neighbouring public road.

Quote from Jacob Aaby Rechendorff in Per Aarsleff AS:

“This was the first time I had worked with RD piles.
The design of wall and anchors was delivered by our in-house design & engineering team in Aarsleff.The engineers had chosen to install the wall as an interlocked retaining wall, consisting of RD600 piles from SSAB. The challenge was to get the wall completely waterproof. By using the RM/RF interlock system with bitumen the wall was watertight. It was only during the anchor work that water came through the wall.

With this drilling method we could keep the vibrations far lower than the given limit value.
The interlocked retaining wall performed according to its design, very slight deflection in the wall during the excavation, well below the tolerances.

The collaboration with SSAB was good, delivery 'just in time' worked exactly as it should, which was important as it was not possible to store many RD piles on the construction site at a time.”