SCOPE

Project: Foundation construction for a 30MW wind power farm including 10 wind power turbines, 2 onshore and 8 offshore.

Project description: The project included channel dredg-ing, underwater drilling and blasting, cast in situ quay wall elements, transport of fi lling materials, deep compaction and revetments of artifi cial islands. Additionally cast in situ founda-tion structures and installation of quay wall elements as well as backfi lling of cable trenches were a part of the scope. The project applied new kinds of working methods, such as tem-porary storage in water areas, and barge-mounted concrete transport containers.

PROJECTLEAFLETKEMI WIND FARM, FINLANDFOUNDATION CONSTRUCTION FOR A 30MW WIND POWER FARM

Terramare Oy

Laurinmäenkuja 3 A

PO Box 14, FI–00441 HELSINKI, FINLAND

P +358 9 613 621 | F +358 9 6136 2700

www.terramare.fi PAGE 1/4

FEATURES

Client PVO–Innopower Oy (Since 2011, Innopower Oy)

Location Ajos Harbour, Kemi, Finland

Period November 2006 – September 2008

Contractor Terramare Oy

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Aerial view of the southern part of the project area on 2007.

The artifical islands were constructed offshore in 3–8 metres deep water.

INTRODUCTION | QUANTITIES | MAIN PLANT >

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QUANTITIES

Dredging 15,000 m3

Underwater drilling and blasting 1,000 m2

Retaining quay wall 376 m

Coping beam 376 m, h = 5.45

Erosion protection slab 1,500 m2

Concrete in total 6,970 m3

Blasted rock fi llings for artifi cial islands 214,000 m3

Deep compaction of the rock fi ll 13,650 drops

KEY FIGURES OF THE ARTIFICIAL ISLAND

Area 30 x 50 m

Rock fi lling 23,000 m3

Rock revetment 3,000 m3

Geotextile 6,000 m2

Concrete 700 m3

Number of artifi cial islands 8

INTRODUCTION

Foundation work for the Kemi off-shore wind farm started in Novem-ber 2006. When the wind farm was completed in late 2008, it was the largest one in Finland. The overall project included the construction of a 30 megawatt

wind power farm, consisting of ten wind turbine power sta-tions of three megawatts each. Most of the foundation work took place offshore, where a total of eight artifi cal island foundations were built including maintenance quay walls and erosion protection. Two wind turbine foundations were also built onshore. In many ways the project represented an experiment in which a workable model was sought for build-ing of similar wind farms in the future.

Dredging, Underwater Drilling and Blasting

The project started with preparation of foundation works onshore including construction of the roads. Dredging and underwater drilling and blasting of channels for the project barge traffi c were executed. The need for fairway works was quite substantial, because of the location of the ar-tifi cial islands 0.5–4 km away from the port of Ajos. The width and depth of the channel had to be large enough for busy and heavy traffi c during the project and also for the future maintenance of the power stations. Channel work proceeded rapidly and the construction of the artifi cial is-lands began on schedule.

Construction of Artifi cial Islands and Foundations

The artifi cal islands were constructed offshore in 3–8 me-tres deep water. On average, 23,000 m3 of blasted rock was needed for one artifi cial island, which meant the trans-portation of nearly 1,000 truckloads of rock to the port of Ajos. Moreover, around 3,000 m3 of rock revetment was required for fi nalization of the artifi cial islands.

A new solution, in which loads of blasted rock were tipped into the harbor basin, was used as a temporary storage point for the fi lling material. Backhoe dredger loaded ma-terials from the temporary storage point onto the barges for further transportation to the sites. In addition to saving time, an advantage of the underwater storage was also the fact that stone dust was prevented from spreading into the

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environment. It was possible to begin the reclamation work in summer, and this was so effective that some of the fi llings were completed earlier as scheduled.

The blasted rock was compacted on the island, after which the foundation was constructed. A heavy, 17 tonne, foundation cylinder was installed in the centre of founda-tion construction. Maintenance quay including protection structures were also built for the artifi cial island. The quay wall elements were prefabricated in the harbour area. The maintenance quay was very signifi cant because it had to enable the access for the heavy 700 tonne crane required for lifting the parts of the power plant.

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LOCATIONS OF THE KEMI WIND FARM UNITS

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All artifical island foundations were built including mainte-nance quay walls and erosion protection.

Eight of the ten turbines were built on artificial islands. Two were built on land. The steel towers of the 3 MW turbines are 88 metres high with a rotor diameter of 100 metres.

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Ten 3 MW turbines. Total capacity 30 MW.

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KEMI WIND FARM, FINLANDFOUNDATION CONSTRUCTION FOR A 30MW WIND POWER FARM

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Terramare Oy

Laurinmäenkuja 3 A

PO Box 14, FI–00441 HELSINKI, FINLAND

P +358 9 613 621 | F +358 9 6136 2700

www.terramare.fi

Concrete Transportation by Sea

The around 500m3 of continuous concreting for the founda-tions was achieved in connection with concrete transport by using containers installed on the barges. This method enabled the concreting to be executed smoothly. A steel container with a capacity of 30 m3 was installed on two of the barges for transportation between the harbour and the island. When the concrete work had been completed, the slopes of the island were protected with crushed aggregate and rock revetment.

Project Objectives Achieved

The project was completed in September 2008, by which time all power plants had also been installed. The project also included underwater drilling and blasting of trenches for the connection cable between the power plants. The fi rst power turbines of the Ajos wind farm started operating in October 2007. The wind farm was inaugurated on 29 Feb-ruary 2009.

MAIN PLANT

Backhoe dredgers Kuokka–Pekka 2, Marika

Self propelled barges Adam, David, Cara, Tiukka

Floating crane Nosto–Pekka

Drill platform Pora–Eero

Work platforms Paalu 1, Pora–Pekka 4

Tug Retu

Main Plant Used on the Project

Terramare’s own plant was used on all project locations. The dredgers Kuokka–Pekka 2 and Marika were used for channel dredging and handling of fi lling material. Under-water drilling and blasting was carried out by the drill plat-form Pora–Eero. The barges Adam, David, Cara and Tiukka were used for the transportation of the fi lling materials. The quay wall elements for the artifi cial islands were installed by using the fl oating crane Nosto–Pekka. The work platforms Paalu 1 and Pora–Pekka 4 were used for transportation of equipment and supplies to the artifi cial islands. At the same time, they also were utilized as work pontoons. The tug Retu was used for towing operations and for crew changes.

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E Aerial view of the Kemi Wind Farm.

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