Lessons learned from the 2015 Soerkjosen shoreline landslide in Norway

Soft and partly sensitive clays along the fjords of northern Norway pose a challenge for infrastructure. Learning from failures is essential in providing guidelines for future geotechnical work in such areas. A shoreline landslide with a volume up to 1.4 million m3 took place close to Soerkjosen in northern Norway during the night from the 9th to the 10th of May 2015. The shoreline slumped into the sea over a distance of more than 1 km and parts of a harbor were destroyed. No persons were killed, but after the slide the traffic had to take a 700 km detour through Finland to pass the site. The slide took place in a fjord with steep mountainsides and a large river delta. There was ongoing road construction prior to the event, including rock blasting. The authors of this paper took part in the investigation group that concluded that the stability was lowered to a critical level already in November 2014 when a breakwater / embankment was widened by filling crushed rock into the sea for a road crossing. The actual slide was, however, finally triggered by heavy rain and snow melt half a year later. The lesson learned is to do sufficient ground investigations in such settings. In this case a rather deep, weak clay layer was missed and not taken properly into account in geotechnical design.