The Kirismäki interchange, which is a part of the E18 Turku ring road improvement project, is a pilot site where Peikko's PSB® Punching Reinforcement System was used for the first time in a road's pile-supported slab structure to strengthen the connection points of foundation piles and concrete slab.
Road network and the related intersection construction projects are often huge in size, and their construction may take years. That is why technical solutions that speed up the construction and improve cost-efficiency are very welcome.
In Finland, the European road E18 goes through the whole of Southern Finland, in the east from the vicinity of the Russian border to Turku on the west coast of Finland. On the ring road passing Turku, traffic flow will be improved when one section of the road is constructed to have four lanes in Finnish Transport Infrastructure Agency's road improvement project. At-grade intersections will be eliminated and replaced by an overbridge at Kirismäki interchange improvement.
New solutions for the needs of infrastructure construction
Peikko proposed a totally new kind of a solution for the pile-supported slab to the Finnish Transport Infrastructure Agency. The starting point was to establish how the ETA approved PSB® Punching Reinforcement System, which has long been used in building construction, could simplify the strengthening of the roadbed's pile-supported slab.
After preparing the design criteria, a trial use permit was received for the structure, and the Kirismäki interchange was selected as the pilot site. The solution was implemented together with the Finnish Transport Infrastructure Agency, WSP Finland, who were responsible for designing the pile-supported slab structure, and Destia as the main contractor.
"Peikko wants to be a significant supplier of fastening and connection technology for infrastructure projects. New innovations are sought, both by applying solutions that are familiar in building construction, as well as by developing completely new solutions. The development work is most fruitful when it is performed in close cooperation between the developer, designers, and constructors," says Topi Laiho, Business Manager for Peikko's infrastructure construction.
The pile-supported slab was strengthened with punching reinforcement
At sites that require pile-driving of the roadbed, the pile-supported slab is usually implemented as a so-called mushroom slab structure. In it, the connections between the piles and the slab are strengthened using a concrete bulge, which is cast on the upper part of the pile and which, together with the pile, strengthens the concrete slab cast on top of it.
The functioning of Peikko's PSB® Punching Reinforcement System is based on the excellent anchoring characteristics of the product. Reinforcement rails form a star-like structure inside the concrete slab. It is fastened with thin binding wires into the slab's concrete reinforcement above each pile.
The advantage of this solution compared with a mushroom slab structure is speed. Construction can be implemented directly to the level ground. Thus, there is no need to mold holes needed for casting concrete reinforcement around the piles, which significantly shortens construction time.
Costs of the solution are optimized in the design phase
WSP Finland's designer and Project Engineer Jaakko Ingerttilä says that the design of a pile-supported slab requires multidimensional optimization. The aim is to achieve the best possible cost-efficiency. In the design, for example the type and bearing capacity of the soil, as well as the load and elevation of the road structure, are taken into consideration. These factors have an impact on the selection of the pile type and on the positioning of the piles beneath the slab. In addition, the property class of the concrete in the slab, slab depth and reinforcement are optimized.
Design of the pile-supported slab for the Kirismäki interchange
In the Kirismäki project, reinforced concrete piles were used. Because of the thick clay soil, the aim was to minimize the number of piles. When there are fewer piles, a great force of the pile load is impacted on the connection of the pile-supported slab, and the pile tends to punch through the slab. It is possible to increase the slab's punching resistance by making the slab thicker, using shear reinforcements, or by changing the concrete strength.
In the pilot project, one section of one pile-supported slab was implemented using the PSB® Punching Reinforcement System instead of a mushroom slab. This was the first time that this Peikko's System was used in a pile-supported slab project. Peikko provided design support as well as guidance in the use of the Peikko Designer® software.
"Together with the Finnish Transport Infrastructure Agency, Peikko has performed good work with the design criteria," Jaakko Ingerttilä mentions.
"The punching reinforcement dimensioning methods that are in use in Finland are based on the Finnish building regulations, whereas the dimensioning of the PSB® Punching Reinforcement System is based on Eurocode and the ETA assessment of the product. There are slight differences between these and for this reason, my understanding is that with Peikko's PSB®, it is not possible to achieve slabs as thin as might be possible. We have presented Peikko with a development idea in this area."
Destia compares the benefits of pile-supported slab structures
In the Kirismäki interchange, both the traditional mushroom slab and Peikko's PSB® System were used to compare the functioning and cost impacts of the solutions. At Destia, the comparison of the pile-supported slab structures is performed by Panu Salminen, foreman:
"The punching reinforcement system speeds up the construction of a pile-supported slab significantly, because one work phase, namely the holes made for the mushroom structures and concreting these, is eliminated. This can speed up the work by up to a week." Installation of the punching reinforcement was really easy and fast according to Panu Salminen.
The use of the punching reinforcement system does, however, require a thicker concrete slab. In these types of projects, the depth of a mushroom slab's concrete slab is usually 25 cm (10 in) and at the mushroom bulges, 53 cm (21 in). In the case of Kirismäki punching reinforcement system, the slab depth was 41 cm (16 in). On the basis of the pilot project's comparison calculations, design criteria for reducing the slab depth can be reassessed.
Project facts:
- Developer: Finnish Transport Infrastructure Agency
- Structural Designer: WSP Finland Oy
- Main contractor: Destia Oy
This article has been originally published in Connections 1/2021 customer magazine. Read Peikko's customer magazines here: Connections customer magazine