Background

The railway section between Seinäjoki and Oulu is one of the busiest railway sections in Finland, and it is also part of the entire trans-European TEN-T transport network. In the middle of this section of the line is Ylivieska station, which is an important crossing and stopping point for both passenger and freight traffic.
At the southern end of Ylivieska railway station, directly below the tracks, is a more than 100-meter-long, two-hole stone access areas with a capacity of more than 200 cubic meters.

The problem with old access areas is often that the soil around them is slowly leaking from the joints of the stones inside. This creates voids, causing the roads and tracks above to begin to sink over time. Vibration and rainwater from trains running on the tracks often exacerbate the subsidence problem. This was also the situation in Ylivieska.

Depression affects the geometry of the tracks, which is always a safety risk and forces speed limits to be imposed on the tracks. In Ylivieska, some of the voids had already grown so large that they reached the surface.

As the access was no longer needed, the Finnish Rail Administration, which is responsible for the maintenance of Finnish roads, railways and waterways, wanted to decommission the stone area altogether instead of repairing it. To this end, the Finnish Rail Agency asked Geobear for a proposal that could be implemented entirely with and without disruption to rail traffic.

Geobear has a wealth of experience in filling voids of different sizes and compacting structures. As a solution, a filling method was proposed in which swellable geopolymers are utilized together with Leca gravel.

Customer alternatives

Old, decommissioned stone access areas have traditionally been filled with concrete. In this case, however, the concrete filling was not the optimal solution due to the length of the stone drum. The works would also have interrupted the rail traffic, at least in part, as the concrete filling could not have been carried out without opening the route from above.

Geobear solution

Geobear’s goal was to close the decommissioned area permanently so that no more soil could leak into it and no more voids or depressions would form above it. Geobear designed a solution for the project in which a 205 m³ void was filled with Leca gravel and geopolymer resin.

The area under the yard consisted of two openings of the same size (90 cm wide and 125 cm high), the features of which were mapped using, among other things, a drone equipped with a camera.

The blowing of Leca gravel and the injection of geopolymer was carried out in work steps of 6m in length, so that the Leca gravel, which was first blown into an area of 3m in length, acted as a “counterpart” to the expanding geopolymer. The purpose of the geopolymer was to compact the Leca filling, fill the voids between the two tunnels and thus ensure a 100% filling rate. The team also made sure that the access openings were filled alternately at the same rate, which prevented any horizontal movements of the stone.

During injection, the vertical geometry of the tracks on top of the site was monitored in real-time using laser gauges to ensure that the tracks did not rise during the work.
The expanding geopolymer and Leca gravel brought a safe and permanent solution to the problem in the Ylivieska railway area, and this very challenging filling project was carried out in cooperation with the Finnish Rail Agency, Ramboll CM Oy, Winco Oy and Sundström Ab Oy during 7 days of rail traffic and passengers. without disturbing.

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