Residential areas built on clay are sinking in Helsinki area

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Dozens of residential areas in Helsinki, Espoo, and Vantaa have been built on soft clay or marsh soils, which have a high subsidence risk. As the prices for plots of land are high in the Greater Helsinki area, residential properties have been built also on these unstable clay soils, which elsewhere in the country would have been left undeveloped.
     
Signs of subsidence include the appearance of cracks in asphalt, pipe damage, and the disruption of the sewer system.
      Streets and yards tend to form pools and puddles, when the sewage systems that have been underpinned remain uplifted, while the ground is sinking around them. Moreover, rain water can also slip beneath buildings.
     
Currently, the problems of subsidence and their implications for buildings are being encountered particularly in Helsinki's districts of Kannelmäki, Pikku-Huopalahti, and Itäkeskus, as well as in Vantaa's Tikkurila, and in a number of areas of Espoo, including Perkkaa (Leppävaara), Matinkylä, Olarinluoma, and Espoon Keskus .
      While similar problems are very seldom encountered by apartment buildings, it is typical for the detached houses that have been built on clay without being underpinned to be gradually sinking in the course of decades.
     
Compared with previous years, more attention is today being given to the underpinning of the soil. However, the yards around some apartment buildings are still being built directly on clay.
      On the other hand, it has become customary in Helsinki to prevent the problems of subsidence in advance by underpinning the entire area covered by the city plan. The costs are then included in the prices of plots to developers, while in Vantaa, the problem is laid at the door of building constructors.
      "While still in the 1970s no sensible methods existed to support shrinkable clay soils, the modern pillar stabilisation can be carried out at a reasonable cost", says Manager Harri Tanska from the City of Espoo's Geotechnical Division.
      "Typically, the building constructors want to spend only a minimum amount of money on yards. Moreover, as the period of guarantee is only ten years, and no major subsidence problems might occur within that time", Tanska concludes.


Previously in HS International Edition:
  Climate change: more mild and rainy winters in store for Finland (22.2.2005)

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