RR270 and RR320 piles with new rock shoes to Kupittaan Parkki in Turku, Finland
October 01, 2021 9:32 CEST 6 min read
New mechanically attached rock shoes for RR270 and RR320 pile sizes ensured more flexible piling works at Kupittaan Parkki site.
YIT is building a new multi-story parking facility for Turku Technology Properties to Kupittaa area in Turku, Finland. The location is just next to Kupittaa railway station and Turku Science Park. Turku Science Park is area where several office buildings and university buildings are located. These buildings are for example BioCity, DataCity, ICT-City and new campus of Turku University of Applied Sciences. The area has been lacking of parking places for many years and this new building is answering to that need.
Figure 1, Illustration of Kupittaan Parkki (image courtesy Schauman Arkkitehdit)
New parking facility will have 10 storeys and area of almost 30 000 square meters for about thousand cars and 90 bicycles. Main part of the parking places are long term rented, but there will also be parking places for short term parking and a roofed connection to Kupittaa railway station.
High strength steel piles for high concentrated loads
Parking of cars requires as open space as possible. This leads to structures with long spans and columns as vertical structures. Together these mean high concentrated loads to foundations.
With SSAB’s high strength S550J2H steel grade the design resistances of piles can be higher than with standard S460MH steel grade. This offers possibility to use smaller pile sizes and/or to reduce amount of piles. In Kupittaan Parkki case the resistance offered by high strength steel was fully utilized.
Three pile sizes RR140/10, RR270/12.5 and RR320/12.5 (S550J2H) were used in the project. RR140/10 piles were installed with hydraulic ram and larger piles were installed with 7 ton hydraulic hammer. 7 ton hammer was used to enable PDA testing with same driving equipment. RR320/12.5 pile size made of S550J2H steel grade was used in places with highest concentrated loads.
All piles were driven against the bedrock and the resistances of the piles were verified with PDA measurements in the beginning of the work. Totally 16 piles (5 pcs of RR140/10, 3 pcs of RR270/12.5 and 8 pcs of RR320/12.5) were installed to different locations around the building site and tested with PDA. All these test piles are also working as part of the final piling.
Figure 2, Results of PDA measurement for pile number 215, pile size RR320/12.5 (S550J2H). RMX of appr. 6400 kN was mobilized during the PDA measurements
New mechanically attached rock shoes offered cost efficiency
RR270 and RR320 piles were equipped with new mechanically attached rock shoes which were introduced in 2021. These rock shoes have been tested and approved also for piles made of high strength S550J2H steel grade. Use of higher steel grade for piles sets also higher demands for rock shoes. Rock shoes need to have high enough resistance also for possible PDA tests, where the stresses in the piles are at the limit.
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Figure 3. New rock shoe attached to pile pipe, final tightening will happen during driving of pile.
Beside just resistance, in this case the mechanically attached rock shoes offered also other advantages compared to old rock shoe models attached by welding. The lengths of the piles were varying from about 4 meters to close to 10 meters. Piling contractor decided to use 12 meter pipes at the first place and then continue by using cut parts from previously installed piles. This naturally offers savings, but also requires rocks shoes which are able to be attached to piles on site.
With welded rock shoes this would have been very difficult due to demanding attachment welding on site conditions. New mechanically attached rock shoes provided a fast and cost efficient way to use cut parts of previously installed piles.
Raking piles defined piling order
In the middle of the building each pile cap has totally eight RR320/12.5 (S550J2H) piles. In most cases all these piles are raking piles. Raking piles were directed so that piles are spreading downwards. This together with cutting level of piles being sometimes below existing ground level defined working order for piling.
Figure 4. Installation of a raking RR320/12.5 (S550J2H) pile.
For pile caps where the cutting level of piles was below existing ground level, it was possible to install only six of the piles before cutting. The top parts of uncut piles prevented installation of all piles. Remaining two piles were installed after excavation and cutting of piles.
Figure 5. In some places the cutting level of piles was below ground level.
Demanding soil conditions
Part of the building area had very demanding soil conditions. Soil layers were partly old fill layers with old concrete retaining wall just next to the new piles. Natural soil below these man made layers contained some stones and boulders and also the surface of the bedrock had steep formations. Quite often RD piles are chosen for such conditions.
Piling with driven RR piles in such conditions requires good understanding from piling rig operator. Piling rig operator Janne Haapasalo from Turun Siirtomurske Oy has over 25 years of experience in pile driving with several different piling equipment. “Piling is not a matter of force, even though the equipment is heavy and powerful” says Janne, and continues “Most often much better results are achieved with little less force and little more understanding”.
RR140/10-E S460MH 840 m
RR270/12.5 S460MH 288 m
RR320/12.5 S550J2H 1632 m
Project owner: Turku Technology Properties
Main contractor: YIT Rakennus Oy
Contractor for piling and earthwork: Turun Siirtomurske Oy
Geotechnical designer: SM Maanpää Oy
Structural designer: SRT Oy
More information on RR® and RD® piles and RD® pile wall www.ssab.com/infra