Numerical Methods in Geotechnical Engineering – Hicks, Brinkgreve & Rohe (Eds) © 2014Taylor & Francis Group, London, 978-1-138-00146-6 A preliminary study of rheological models for run-out distance modelling of sensitive clay debris V. Thakur Norwegian Public Roads Administration, Norway Aalesund University College, Norway D. Nigussie & S.A. Degago Norwegian Public Roads Administration, Norway ABSTRACT: Estimating the extent of post-failure movements is vital in the context of hazard mapping, preparedness and mitigation strategies. The current practice is limited to simplified empirical approaches which are mainly attributed to poor understanding of the mechanisms associated with the post-failure movements of sensitive clay debris. In this work, a 3D numerical tool mainly used for the dynamic analysis of rapid landslides and rock avalanches (DAN) has been adopted to make a preliminary study on run-out modelling of sensitive clay debris. In doing so, a recent case of a flow slide in Norway is used as a reference to evaluate numerical predictions. Results are discussed in light of the field data for a sensitive clay flow slide. 1 BACKGROUND Flow slide in sensitive clays deposits of Scandinavia is a well-known geo-hazard. Consequently, the ret- rogression and the run-out of sensitive clay debris pose a serious risk to human lives, infrastructure, and sensitive ecosystems within their range (Figure 1). Therefore, accurate prediction of flow slide behaviour, including retrogression distance, run-out length and flow velocity, is essential for hazard risk assessment. Although the estimation of landslide retrogression in sensitive clays has received considerable attention, an appropriate numerical method for investigating the run-out of sensitive clay debris remains a topic of research. 2 INTRODUCTION Various literature, e.g. Mitchell and Markell (1974); Corominas (1996); Rickenmann (1999); Fell et al. Figure 1. Run-out of sensitive clay debris (Thakur and Degago, 2014). (2000); Fannin & Wise (2001); Legros (2002); Vaunat & Leroueil (2002); Bathurst et al. (2003); Crosta et al. (2003); Hungr 2005; Locat & Lee (2005); L’Heureux (2012); Thakur & Degago (2013) proposes various analytical and empirical relations to estimate the retrogression and the run-out distances. Thakur et al. (2014) present a comprehensive sum- mary of various approaches adopted for the estimation of run-out distances based on geometrical aspects and individual soil parameters such as; remoulded shear strength, liquidity index, quickness, soil sen- sitivity. They emphasised on the limited success of the empirical correlations derived from an individ- ual parameter and advocated on use of integrated approaches that take into account a wide range of geotechnical parameters. Numerical modelling of run-out distance of sen- sitive clay debris has so far received a very little focus. Different approaches and methods have been developed in the past for a quantitative risk analysis using dynamic run-out models for debris flows and avalanches. Some of the commonly used models to estimate run-out distances are quasi-two-dimensional numerical models (e.g., BING (Imran et al. 2001) and NIS (Norem et al. 1987)) and quasi-three-dimensional models (e.g., DAN3D (Hungr 1995; McDougall & Hungr, 2004), MassMov2D (Beguería et al. 2009), LS-RAIPD (Sassa 1988) and RAMMS (Christen et al. 2002). However, none of these tools are specifically developed for the estimation of the run-out distance of sensitive clay debris. This can be perhaps attributed to, among other factors, an insufficient knowledge about the complex rheological behaviour of sensitive clays 115