Erroneous data in the E6 landslide at Stenungsund, Sweden? – GWC Mag

The Landslide Blog is written by Dave Petley, who is widely recognized as a world leader in the study and management of landslides.

Back in September 2023, I posted about an interesting and very large landslide that had destroyed a section of a key road – the E6 motorway at Stenungsund in Sweden. At that time I speculated that the cause might be loading of the head of the landslide, a mechanism that is broadly similar to the recent Nordic Waste landslide in Denmark.

Shortly after the accident, which injured three people, loyal reader Anton Larsson tweeted some great images of the failure:-

The failure is currently under investigation by both the National Accident Commission and the police, so we await a definitive report. But, a news agency in Sweden, SVT, has a series of very interesting reports on possible causes of the landslide. The reports are in Swedish, but they are easily translated.

In the upper portion of the slope, a business park was under construction at the time of the landslide. To build a platform, the ground was elevated with up to 6 metres of fill, which loaded the head of what became the landslide.

According to SVT, advice was provided to the team constructing the site about the potential stability of the slope by the Swedish Geotechnical Institute. In this particular part of the slope no boreholes were drilled (it will be interesting to know why), and the desktop data indicated that the rockhead was close to the surface. This led to an assumption that the ground was able to carry the additional load without stability issues. The report indicates that the underlying error may have been as simple as a line on a map:-

In the news reports, it is alleged that the Swedish Geotechnical Institute would have recommended drilling at the site if there had been doubt about the presence of solid rock. If this report is correct then a simple misunderstanding may have put in place the chain of events that led to this very serious landslide.

Of course, these initial reports are speculative, and we await the outcome of the formal investigations, but there is much to learn from this very interesting landslide.

Meanwhile, reconstruction of the E6 at Stenungsund continues, with an expectation that the road will reopen towards the end of this year or in early 2025. The scale of the works is huge – for example, 30,000 tonnes of soil has had to be removed.

Acknowledgement

Thanks to Anton Larsson for highlighting these news reports via Twitter.

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