WP4: Retrogression and runout analyses of sensitive clay landslide
Landslides in sensitive clays pose a major socio-economic threat to population, infrastructure, property, and the environment because of their retrogressive characteristics and extreme mobility.
A recent example is the fatal sensitive clay landslide at Ask in Gjerdrum in Norway on December 30, 2020. The landslide caused 10 fatalities and destroyed over 31 dwellings, with a runout distance of approx. 2 km (Figure 1). Therefore, an improved understanding and modelling of the retrogression and mobility would help assess potential affected areas for landslides in sensitive clays more accurately, thereby leading to better hazard zone identification and mapping.
Figure 1. Area affected by the quick clay landslide at Gjerdrum, Norway, that occurred on the 30th of December 2020. (Photo credit: NGI – Håkon Heyerdahl)
The main tasks of this study are to investigate the effect of various factors, including softening, anisotropy, shear rate and mesh dependency, on the retrogression and mobility behaviours of sensitive clays. Additionally, the study will develop advanced numerical models (total stress and/or effective stress-based) for quantification of retrogression, lateral spread, and runout distances in sensitive clays. These models will be compared with historical landslide events to validate the accuracy of the retrogression and runout analyses. A preliminary attempt using the Material Point Method has been made in the study, as shown in Figure 2. The challenge lies in developing a realistic numerical framework that can capture the unique behaviour of sensitive clays and finding representative soil parameters to use in the numerical analyses.
Figure 2. Shear band development of the simulated Gjerdrum landslide. Red curve is the sliding surface interpreted from the in-situ CPTUs
Zhongqiang Liu
Senior Specialist Slope Stability and Risk Assessment zhongqiang.liu@ngi.no+47 479 29 799