The floor of the protected hangar of Malmi Airport has collapsed

Jun 8, 2023

The soil at Malmi Airport is shifting

The floor of the protected aircraft hangar at Helsinki-Malmi Airport has collapsed. The earth masses under the ground based floor have apparently started to move due to the excavation and piling works carried out in the area and the vibrations caused by them. Several of the protected building’s large, hexagonal floor tiles have been badly cracked, and the hangar floor has already sunk up to 20 centimeters in some places.

During aviation operations, the area’s surface waters have been controlled and the drainage of the traffic area has been kept in working order, even in winter, for more than 80 years. The maintenance ended when the city took over the field. The natural gas pipeline routes dug into the field have disturbed the soil’s surface water and groundwater relations. The flow of pressurized perched groundwater, at a depth of about one meter, has also been disturbed. According to an expert’s assessment, the water sprayed around to freeze the new ice skating rink in winter could have worsened the situation even more.

It is common knowledge that the consequences of changes in groundwater conditions in clay soil are completely unpredictable. Generally, the soil then sinks. The risk has inevitably been known to the land construction operators and experts used by the City of Helsinki.

The Friends of Malmi Airport (FoMA) has repeatedly warned about the soil risks related to the deep muddy clay of the area. The civil engineering expert, M.Sc. Lasse Minkkinen, states that the predictions have come true in the worst possible way.

“In such clay, it is very common for the soil to move laterally along sliding surfaces, causing the ground level to drop. This has apparently happened in this case as well. In general, this kind of soil needs piles one meter apart. The surface of the soil may also rise somewhere else.”

An experiment has been made to stabilize the airport area with lime columns. This can stiffen up the soil somewhat. However, the soil in the airport area is up to tens of meters deep muddy clay, and deposits of sulphide clay have been found there. When it oxidizes with air, it forms sulfuric acid, and when it starts to move, it weakens the stabilizing columns.

Minkkinen has investigated the matter:

“The piling depth can be up to 30 meters in the airport area, and depths of over 70 meters have been found in the neighboring Tattarisuo area. The limestone pillars are not reinforced, and especially the longer ones may buckle.”

Residential areas built next to the airport area are in the same geological area. In Fallkulla, the soil has subsided significantly, and the foundations of the houses have needed repairs. Similar changes have also been observed in Alppikylä.

Chairman of Friends of Malmi Airport Håkan Lövdahl demands immediate corrective measures.

“The City of Helsinki has a responsibility to restore the building protected in the zoning plan and to prevent similar damages from happening in the future. It has become clear that the area is not suitable for housing construction. Its use must be re-evaluated, preferably as an airport.”

More information about the history of the hangar:

Internationally acclaimed heritage site: Heritage values of Malmi Airport

The pictures below may be used freely in reporting the matter, mentioning the source:

The deep and wide trench dug in 2022-2023 for the main natural gas pipeline (in red) tore open the muddy clay in front of the hangar along its entire length and damaged the large-capacity drainage system built in the 1930s. A significantly less expensive alternative (in blue) utilizing the old, perfectly functional pipeline was not taken into consideration. All the construction marked in shades of brown on the plan map only exists on the drawing board.