Finland’s largest ever dredging contract: rocky ground and extreme cold

Boskalis is involved in two major port extension projects in Finland. The project in Raahe was completed in December 2009, while work started in Hamina in July the same year. Works manager André van der Wiel (Raahe) and project manager Gert Jan Peters (Hamina) told us about their experiences in a country where the extremely cold winter weather and the rocky ground generated exceptional challenges. Finland is part of Boskalis’ Nordic home market. The dredging company Terramare Oy, which has been the Boskalis local trump card in Finland since 1998, was awarded the Raahe project in late 2007. The clients are the municipal authority of Raahe and the Finnish Maritime Administration. “It’s the largest dredging contract in Finnish history,” says works manager André van der Wiel, with a hint of pride. “Important clients, such as the steel company Ruukki, want to provide facilities for larger ships so the entrance channel had to be deepened and the harbor extended.”

No delay

The first phase of the project started in Raahe in February 2008: the construction of a bund measuring two kilometers. The dredged material from the harbor basin was pumped behind the bund, creating new land. Dredging work, to extend the port to a depth of 11.5m, followed in June 2008. The project produced a total of two million cubic meters of dredged material, some of which was recycled for land reclamation. The cutter Jokra was deployed to dredge the basin, removing the soft upper layer and as much of the moraine layer (sand, clay and stones) as possible, before pumping it through a floating line to the right location, behind the bund. The backhoes Attila and MP27 then dredged the harder layers below. The dragline Manitowoc was deployed to take this material onshore, working in combination with an unloading quay with a hydraulic crane. Rock was removed using Terramare’s ‘drilling & blasting’ pontoon.

Bunking down for the winter

“During the winter months, work continued for a long time, but when the temperature dropped to -20°C, everything came to a halt. It was still possible to work on in the harbor basin, where the cooling water from the steel factory warmed up the water. To make most of this opportunity, it was decided that the Attila would stay for the winter. That turned out to be a good decision: the other ships only managed to sail in on 22 May, but the Attila was already back at work in early April,” recalls André. The final part of the project involved the 200m wide, 10km long entrance channel. A total of 1.9 million cubic meters of material was dredged from the channel, to deepen it by two meters to a depth of 11.5 m. This phase was completed in October 2009 by the backhoes Nordic Giant and Koura, and the bucket dredger Ajax. “During this phase of the project, we regularly dredged up boulders. And big ones too,” André explains. “One boulder measured 43m3.” The Nordic Giant lived up to its name by removing the boulders with her 18m³ bucket.

Bar sweeping

Before completion, ‘bar sweeping’ took place in both the channel and the harbor basin. This is a typically Scandinavian approach used to provide a 100 per cent guarantee for the agreed depth. A steel bar is lowered to the required final depth. In this way, any unwanted shallow spots are traced extremely effectively, and extra dredging takes place to remove them. However, our dredging methods kept this to a minimum. “The Raahe project was completed in December 2009, and the customer is very happy,” says André van der Wiel. A lot of equipment, including the Nordic Giant, was then sent on to the next Finnish harbor project: Hamina.

Hamina start in July

Hamina, which is close to the Russian border, in southeast Finland, is a homeport for the oil industry and a transit harbor for timber, cars and other goods on their way to Russia. Just like Raahe, it wants to provide access for larger vessels, and so it has to make changes to the port and the entrance channel. Terramare won this assignment in late 2008. The clients are the municipal authority of Hamina and the Finnish Maritime Administration.

André van der Wiel & Gert-Jan Peters, Royal Boskalis Westminster N.V., Papendrecht, The Netherlands
Edition: Edition 45

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