Date of occurrence:
O-9/23
A large landslide on the E6 road outside Stenungsund, Västra Götalands County
Summary in English
On 23 September 2023 at 01:39 a landslide occurred east of the city of Stenungsund, Västra Götaland County. The landslide caused extensive infrastructure and property damage, and damage to the environment. Three persons were injured, but no one was seriously injured.
The landslide started in the eastern part of the affected area on the property Stenungsund Hammar 1:14 and spread further towards the north-west. The landslide affected an area of 600 x 400 metres.
Development work had been carried out on the property Stenungsund Hammar 1:14 between May and September 2023. The fill masses added to the property caused an overload of the ground. The overload caused the clay to collapse, which in turn initiated the landslide. The development work resulted in the addition of almost ten metres of fill masses compared to the previous ground level at the western property boundary. The development works were therefore carried out outside the property boundary, with the support slope on natural land and above the height level permitted by the permit given for the development works.
The widespread prevalence of highly sensitive clay and quick clay in the affected area contributed to the extent of the landslide. Natural barriers and lesser clay depths in the southern part of the area limited the spread of the landslide in the south. In the north-eastern part of the affected area, the clay depths were greater, which probably contributed to a greater spread of the landslide in that area. The rain that fell during July, August and mainly September probably contributed to the timing of the landslide, but of significant importance was the overload caused by the fill masses.
The property Stenungsund Hammar 1:14 was included in the zoning plan Munkeröd 1:12 etc., which became legally binding in 2021. The SHK had identified flaws in the zoning plan Munkeröd 1:12 etc. An identified deficiency was that the ground conditions were not fully investigated and the zoning plan therefore did not ensure the land's suitability for the purpose. Another deficiency was that the design of a zoning plan provision concerning the property's height level enabled different interpretations of the provision.
The SHK questions whether Stenungsund's municipality has adopted the risks of landslides and erosion in its operations. Overall, there are reasons that suggest that the municipality should systematically review its assessment and management of geotechnical safety issues in the master and zoning planning processes and the process for development works and building permits.
Finally, SHK can conclude that the government’s support to municipalities in Sweden pertaining landslides and erosion is extensive. Several authorities contribute to increased knowledge and uniform management of geotechnical safety issues. A good example is the inter-municipal collaboration organized by the County Administrative Board in Västra Götaland. It is important that the work of the government authorities continues and develops in line with the needs of the municipalities.
Causes of the accident
The direct cause of the landslide was that the ground on the property Hammar 1:14 was overloaded by filling masses during development work. The rainfall that had fallen likely contributed to when the landslide occurred.
The underlying cause for the ground being overloaded was a lack of consideration for prevailing local ground conditions. The conditions had not been sufficiently clarified before the work began. The following factors have contributed to this:
- The geotechnical investigation that was the basis for the assessment of the suitability of the ground was flawed and contained errors.
- The zoning plan for Munkeröd 1:12 etc. had deficiencies regarding clarity.
- No additional surveys of the land were carried out before the development works began on the property Hammar 1:14.
Safety recommendations
SHK submits the following recommendations:
Stenungsund municipality is recommended to:
- Strengthen their ability to handle geotechnical safety issues and ensure that the strategy announced in the 2020 master plan regarding landslides, landslides and erosion comes to fruition. (SHK 2025:10 R1)
The Swedish Government is recommended to:
- Consider to task the Swedish National Board of Housing, Building and Planning to investigate relevant improvements of the assessment of suitability in Swedish law and the zoning planning process. (SHK 2025:10 R2)
Jonas Bäckstrand
Alexander Hurtig
Page information
- Last updated:
- 17 June 2025