Installing terrace foundations on soft clay soil (CASE: Ankkapuisto Park, Vantaa, Finland)
Ankkapuisto Park in Korso, Vantaa has gone through extensive improvement works which have made the area much more attractive.
As an icing on the cake, and as a pleasant surprise to its users, it was decided that two large public terraces would be built in Ankkapuisto in July 2019. The terraces are also meant to be used as performance stages in various events taking place in the park.
A challenging but quick piling project
Rotopile’s mission in this project was to install the foundations of the terraces into soft clay ground surrounding a pond. Because the layer of clay was thick and soft, the piles for this project needed to be longer than usual. Thus the piling of the Ankkapuisto Park terraces was a bit more laborious than regular terrace piling, but we were still able to complete the project quickly.
The screw piles were installed up to 14 meters deep in 2-6 meter segments. In addition we used extension piles and boltable extension sockets. Although the screw piles used for this project were relatively long, we did still make a saving in the overall cost of the piling. For example, had we used driven piles, that would’ve required an even greater installation depth.
For comparison:
- Typically 60,3 x 2,9 mm screw piles with either 150 mm (HELIX™ and ECO™ series) or 200 mm (PRO™ series) helice would be used to install terrace foundations.
- The size of the screw piles in this project was 88,9 x 6,3mm and the diameter of the helice 250 mm (PRO™-series).
Screw piles this big are an exception in terrace projects, however the size of the piles must always be determined based on the loads and soil type of each project. In this particular project we were installing the foundations into soft clay soil, which required a solution to fit the challenges it brings.
Rotopile has a lot of experience in determining the right size of the screw piles required and we also organise courses for structural engineers in pile sizing.
When should you fill the screw piles after installation?
Out of the norm, it was decided that the screw piles in Ankkapuisto Park would be filled with concrete after installation. This was done because the duck pond situated in the park was lifting water into the pile shafts.
Filling the piles with concrete stopped them filling with water and eliminated the potential risk of the piles splitting when the water would freeze. At times, screw piles are also filled with concrete to improve buckling resistance. This method provides approximately 20% increase in buckling resistance.
All in all, we used over 70 screw piles for the two terraces. The screw piles had a tube size of 88,9 x 6,3 mm and the diameter of the helice was 250mm.
Screw piles are an ideal solution for foundations of structures in parks
The installation machinery used in Ankkapuisto Park was an 8 tonne excavator, which was light enough to keep the areas that had already gone through the improvement work unharmed.
Light machinery, the absence of excavation work as well as low noise levels made screw piling an ideal solution for installing the foundations of these park structures.
Screw piling is also very quick and the building of the framework can start as soon as the piling work is completed. The nuisance caused by the installation to the users of the park was minimal.
Attaching the superstructure to the screw piles
After the screw piles were in place, pile caps with connection sockets were installed on top of the piles, to which the wooden structure of the terraces was easily attached by carpenters.
The style of the terraces is modern and they have been very popular amongst the visitors of the park. All in all, the end product was very successful. The terraces are public and can be visited at Korsontie 11, Vantaa, Finland.
It is definitely worth popping by and visiting the newly renovated Ankkapuisto Park.
