In very challenging weather conditions Danish contractor Per Aarsleff is installing its largest profile and one of its longest combination steel pile retaining walls for the extension to the container terminal in the Port of Muuga on the Gulf of Finland south coast, 17 km east of the Estonian capital Tallinn.
The site team, with its fleet of specialist marine plant, has been coping with freezing temperatures, strong winds and rough seas at the exposed site to accurately drive over 420 tubular steel piles up to 1.67 m diameter and 45 m long into the seabed. Approximately two thirds of these piles, weighing up to 32 tonnes, will be
linked together in combination with pairs of shorter steel sheet piles to form the main combiwall quay frontage and a section of retaining combiwall running parallel with and alongside the terminal’s existing wharf.
One end of the combi sidewall will link into the terminal’s existing quay, while the other end of the main quay will combine with a new 800 m long breakwater joining with the existing natural coastline. The continuous per ipheral combiwall and adjoining breakwater will form an enclosed basin, which is being filled with 1.5 Mm3 of sea-dredged sand to reclaim the new 180,000 m2 extension to the terminal area.
A second line of smaller diameter, equally spaced tubular piles is also being installed behind and parallel to the main berthing wall. Together they will provide the foundation support for the twin rail tracks to take the existing and new quayside container handling cranes.
Joint venture
Muuga Port is the biggest of the several harbours that make up the Port of Tallinn, which is one of the largest ports in the Baltic Sea region. Tallinn Port’s consulting engineers Merin Konsult produced a concept design for the Muuga Port extension, which was based on a twin combiwall of smaller diameter piles.
But Per Aarsleff, in a split joint venture with the Estonian contractor KMG Inseneriehituse AS and the specialist Danish dredging contractor Rohde Nielsen A/S, won the DKK430M detailed design and construct project in open tender with its alternative design. This was produced by its Estonian consultant Estkonsult and based on a single continuous combiwall using much larger diameter tubular steel piles. Per Aarsleff ’s share of the project is about DKK200M, while the remainder is equally split between the other two joint venture partners.
Combiwall piling
The joint venture moved onto site in September 2008 and tarted to attack the project simultaneously on several fronts. Initially Per Aarsleff built up a stock of the huge spirally welded tubular piles each complete with a pair of interlocking clutches welded diametrically opposite on the outside of the tubes.
These were brought in from Holland together with pairs of the interlinking sheet piles from Luxemburg, which were all made and supplied by ArcelorMittal. Piling for the 205 m long combiwall running alongside the existing quay wall started first. This section was constructed by a 130 tonne Liebherr 1130 crawler crane and piling equipment operating from a series of platforms reclaimed behind temporary limestone bunds.
A pair of temporary tubes were first driven with a PVE52 vibrator as deadmen to support a special piling template frame to accommodate up to five of the main tubular piles set at the correct spacing and inline orientation of the interlocks. Each of the main piles was then pitched and driven to level by the PVE52 vibrator followed by pairs of the 10 m long interlinking sheet piles.
The temporary support piles and frame were removed and repositioned to repeat the cycle. Every tenth pile was then struck with a Delmag D62 diesel hammer to a predetermined set to check the required pile bearing capacity of 1,200kN.
