Kundcase

Underpinning of As Oy Matti in Turku, Finland

10 juni 2022 6 min läsning

Information om fallstudien

Produkt RR®- och RD®-mikropålar RD®-foderrör

Land Finland

Företag KFS Finland Oy

Industri Byggnader och infrastruktur

Residential building of As Oy Matti was originally built on end bearing timber piles in the end of 1960s. The level of the building has been followed for some years and the first leveling data is from 2012. During the first years of leveling, the building was in practice non-settling. Since 2016 there has been clear settlement on one area of the building. The settlement rate accelerated during years 2018 and 2019, which emerged the need for underpinning of the building.

Information om fallstudien

Produkt RR®- och RD®-mikropålar RD®-foderrör

Land Finland

Företag KFS Finland Oy

Industri Byggnader och infrastruktur

In the design, the pile type was chosen to be mainly drilled steel pipe pile. Beside drilled piles, also jacked piles were used in few very confined spaces; at the staircases, close to elevator shafts and in boiler room. The most demanding piling work class PTL3 was in use. The pile sizes for drilled piles were RD140/8 and RD140/10 and for jacked piles RR140/8. Totally there were 111 piles in the project, of which 7 were jacked ones. The piling was executed mainly from the basement of the building, where free working height was about 2.2 - 2.4 meters. Due to that, small drilling rigs designed especially for confined spaces were in use. Pile lengths varied between 15 and 27 meters. Pile elements were 1.2 meter long with both ends beveled for splice welding.

Electrically powered drilling rig designed for confined spaces

Drilled RD piles are nowadays the best piling solution for underpinning. With down-the-hole drilling the vibrations for the old structures can be avoided. In addition, the amount of pile points can be minimized when piles are drilled into the bedrock and have high resistances. Fewer piles installed in confined spaces mean lower costs for the end client.

Olli Salviander, NordPile Oy, the site manager of the project

Storage space for pile elements at courtyard

The courtyard of the building is small and there was not enough storage space for pile elements. Pile elements were delivered from SSAB’s mill to NordPile yard, from where the contractor delivered the elements to site in suitable batches according to proceeding of the work.

The locations of the old timber piles were known in rough accuracy according to old designs. Before installation of new piles, the locations were ensured in matter of avoiding contacts with them. Despite of the measures done, the old timber piles caused quite a lot harm for drilling in about half of the area of the building. Totally 41 new piles had contact with old timber piles during drilling. Contact with old timber pile does not prevent drilling of new pile, but it significantly slows down the penetration of the pile. Most often the contacts were small and lasted only short time, but with few piles the contact was more sever and it took long to drill through the old pile. Despite the amount of contacts with old timber piles, only one pile had to be abandoned and replaced with a new pile.

Quality of the bedrock was mainly good. Piles were drilled at least 1 meter into the bedrock. Most of the piles were dry, but some of the piles had artesian water. There was no exact limited area where artesian water was noticed, sometimes totally dry piles were next to piles having quite heavy water flow.

All piles were spliced by welding. Welding was done with a welding robot, which automatically rotates around the pile and is able to weld also in very narrow spaces between piles and old structures. The drill bits were DTH Prime series manufactured by Robit.

In underpinning of existing buildings, the existing technical building services which are in use cause many phases for work. For example water mains, drain pipes, heat exchangers and other services inside old boiler room need to be moved temporarily away from the locations of the new piles. And in the end, those need to be relocated again to new final places. In this project, there was also relatively new heat pump for exhaust air, which was also moved temporarily to another location.

SSAB delivered nearly 2500 m RD pile elements in steel grade S460MH. Consultant for As Oy Matti project was Projektikuutio Oy and geotechnical desigenr was Ramboll Finland Oy. Structural designer for the project was Sitowise Oy and main contractor NordPile Oy (following the acquisition, now KFS Finland Oy).

Existing technical building services in boiler room waiting to be temporarily relocated