Customer case

SSAB steel piles to Finland’s largest piling site

April 01, 2022 6 min read

Case details

Product RR® and RD® large diameter piles RR® and RD® micropiles

Country Finland

Company Metsä Group

Industry Industrial production products

Metsä Fibre, part of Metsä Group, is building a new bioproduct mill in Kemi next to existing pulp mill. The new mill will consume 7.6 million m3 of wood in a year and produce 1.5 million tons of pulp of which 70 % will be exported. Metsä Fibre’s investment to Kemi bioproduct mill is worth 1.85 billion euros and it will increase Finland’s export revenue with 0.5 billion euros annually. SSAB supplied displacement piles and micropiles for this new bioproduct mill, which Metsä Fibre is currently building in Kemi, Finland.

Case details

Product RR® and RD® large diameter piles RR® and RD® micropiles

Country Finland

Company Metsä Group

Industry Industrial production products

Piling work at this site was divided to three phases. In 1^st phase, the piles were mainly RD piles, steel piles installed by drilling. Piling started from the location with the most demanding structure and location. In 2^nd phase, the piles were mainly driven piles, both RR piles (driven steel piles) and precast concrete piles. In the final 3^rd phase, the piles were mainly driven concrete piles. The first piles of this construction site were installed to the foundation of stack.

Before actual piling work, a vast test piling was conducted. The purpose was to compare the suitability of different pile types to project. Test piling was also used to confirm the impression got from geotechnical investigations that the soil is stiff and demanding for driven piles. The soil at the site is post glacial river delta. There is a thick sand layer at the top and silt layer with sulfide below. One particular area had also a rocky mid layer in between, which also resulted in changing from concrete piles to steel piles in that area. In some areas, the bedrock is fractured. There were a total of 1200 – 1300 geotechnical investigations in the area.

The first actions of construction in the area have been made already in the 19^th century, which means almost all top soil is somehow man made. Local specialty is a wooden grid made of laths of wood in wide areas. This wooden grid has been used below sandy top soil to increase the bearing capacity of the soil.

All steel piles were of steel grade S460MH. SSAB’s new RR245 pile size and new mechanically attached rock shoes for RR320 pile size were utilized in the project. In 1^st phase of piling work RR320 pile size was totally replaced with RR245 pile size. The mechanical splices of RR245 resulted in both time and cost savings. RR245 was actually the most used pile size of driven steel piles in the project.

Drilled piles in Metsä Fibes Kemi bioproduct plant. Photo courtesy Nordpile Oy.

We want to cooperate with the best professionals in each field to build a modern bioproduct mill in Kemi. We require our partners to make a commitment to the goals of the project in terms of safety, schedules and quality. SSAB operates in line with these principles, and our cooperation, which began in the Äänekoski bioproduct mill project, is now continuing in another major project.

Eelon Lappalainen, Construction Manager of the bioproduct mill project at Metsä Fibre.

Massive construction work in Metsä Fibre Kemi bioproduct mill in March 2022. Photo courtesy Mitta Oy

Special pile lengths were utilized within drilled piles. Geotechnical investigations by percussion drilling were used to confirm the level of the bedrock at all areas where drilled piles were used. With these results, the determination of exact pile lengths was possible. These pile lengths were used to optimize the manufacturing lengths for pile pipes to ease the installation. Since pile pipes from production were little longer than standard lengths, all drilled piles were done with only one splice weld per pile. Usually standard 12 m long RR pile elements are used for driven piles. In this project longer than standard pile pipes were used also with larger driven RR320 and RR400 pile sizes to optimize the amount of splices. Normal DTH drilling was used for drilled piles. The drill bits were from Robit and Mincon. All splices of drilled piles were done by welding.

The project was the largest piling project in history of Finland. Totally about 140,000 m of steel piles and 550,000 m of precast concrete piles were used in the project. Main piling contractor in the project was NordPile Oy, who had also some subcontractors. At the most totally 11 rigs for driven piles and 4 rigs for drilled piles were in use at the same time. Beside large amount of piling rigs, the work was done in two shifts and partly on weekends. With this amount of piling rigs also service times need to be considered. In practice, with such a large number of machines, a machine was always serviceable.

In a project this big, it is crucial to ensure the availability of piling rigs and pile material well in time. In this case, the discussions with piling contractors as well as steel and concrete pile manufacturers were started already well before test piling phase. Piling work plays a key role, because without piling work, other construction work cannot proceed. It is also important to create a good trust between all parties already in the beginning. Use of standardized design solutions and recognizing of possible bottlenecks in capacities are important. A special project table and timetable template were used in planning. Open dialogue between end client and contractor, mutual trust and respect were in key role in smoothening of high peaks for resources. The result was successful and the required amount of piling rigs and workload for rigs were quite stable throughout the project.

The availability of pile material is always challenging with large projects. None of the pile manufacturers has this large amount of piles in stock. In the supply of steel piles, the supply chain must also be taken into account, all the way from production of steel material to strip rolling and from there onwards to the rolling of pipes and finally manufacturing of the actual pile element. The whole supply chain takes few weeks, which means that possible changes with quantities need to be informed well in time.

SSAB delivered nearly 97 km of RR piles and 42 km of RD piles. Dimension range of RR piles varied from RR170/12.5 to RR400/12.5. RR piles included also pile elements from RR170/12.5 to RR245/12.5 pile element sizes. RD piles were delivered in pile sizes from RD170/12.5 to RD500/12.5.