The final report on the landslide in Stenungsund shows a lack of consideration for soil conditions.
Overloading of the ground combined with a lack of consideration for ground conditions led to the landslide in Stenungsund. This is shown in the final report after the Swedish Accident Investigation Authority (SHK) investigated the landslide that occurred in Stenungsund in Västra Götaland County on 23 September 2023. Alireza Malehmir, professor of geophysics, and Hemin Koyi, professor of geodynamics and tectonics, were hired as experts in the investigation team.
Hemin Koyi, Professor of Geodynamics and Tectonics, and Alireza Malehmir, Professor of Geophysics, during the investigation.
SHK has today published its final report on the investigation. The investigation shows that there is a need for Stenungsund Municipality to strengthen its capacity to deal with geotechnical safety issues.
Causes of the accident
The investigation shows that the direct cause of the landslide was that the ground on the Hammar 1:14 property in the eastern part of the landslide area was overloaded with fill material during ground work. The rainfall that had fallen was likely a contributing factor to the timing of the landslide.
The underlying reason for the overloading of the ground was a failure to take sufficient account of the prevailing local ground conditions. These conditions had not been sufficiently clarified before work began. The following factors contributed to this:
- The geotechnical investigation on which the assessment of the suitability of the land was based was inadequate and contained errors
- The detailed plan for Munkeröd 1:12 et al. was unclear
- No supplementary investigations of the land were carried out before the excavation and filling work began on the Hammar 1:14 property
Press release: https://shk.se/download/18.62650fd19703b9fa2d18dc/1750149934011/O-9_23%20Pressmeddelande%20Stenungsund.pdf
Read the investigation report from the Swedish Accident Investigation Authority: https://shk.se/sok-utredningar/ovriga-handelser/2023-10-03-skred-vid-e6-utanfor-stenungsund-vastra-gotalands-lan
Aftonbladet, news: https://www.aftonbladet.se/nyheter/a/Pplww0/schaktmassor-bakom-skredet-vid-e6
The Swedish Geotechnical Institute (SGI), with support from the Norwegian Geotechnical Institute (NGI), the Geological Survey of Sweden (SGU), the Royal Institute of Technology (KTH), Uppsala University (UU) and COWI Sweden AB, has assisted the Swedish Accident Investigation Authority in its investigation.