IN-SITU DETERMINATION OF DISINTEGRATION ENERGY FOR SOFT SENSITIVE CLAYS

Vikas Thakur, Anders Gylland, Samson Degago, Frode Oset, Rolf Sandven

In the proceedings of: GeoQuébec 2015: 68th Canadian Geotechnical Conference & 7th Canadian Permafrost Conference

Session: Problematic Soils and Ground Improvement II / Sols problématiques et amélioration du comportement II

ABSTRACT: An accurate assessment and prediction of retrogressive landslides in sensitive clays is a complex and demanding task. Still, there have been several attempts to assess flow slide potentials by looking at certain aspects of sensitive clays of which one of them is studying the energy involved in the disintegration of sensitive clays from an intact to a remolded state. This energy is referred to as disintegration energy. Estimation of disintegration energy in the laboratory is not a straightforward task. Moreover, the challenges associated with the sampling of soft sensitive clays complicate the overall picture. Therefore, in this study an effort was made to perform an in-situ measurement of the disintegration process of Norwegian sensitive clays using the electric vane shear apparatus. The significance of the testing procedure and the results are discussed in light of available analytical and laboratory test results. This is also evaluated in light of previous work reported in the literature.

RÉSUMÉ: L™évaluation et la prévision précise des glissements de terrain rétrogressifs dans les argiles sensibles sont des tâches complexes et difficiles. Il y a pourtant eu plusieurs tentatives pour évaluer les potentiels de glissements de terrain en considérant certains aspects des argiles sensibles, par exemple l™étude de l'énergie nécessaire au remodelage des argiles sensibles de l™état intact jusqu™à l™état remodelé. Cette énergie est appelée l™énergie de remodelage. L™estimation de l'énergie de remodelage en laboratoire n™est pas simple à réaliser. De plus, les défis associés à l'échantillonnage des argiles sensibles molles compliquent la situation. Par conséquent, cette étude a évalué le processus de remodelage des argiles sensibles de Norvège lors de l™utilisation in situ d™un scissomètre électrique. L'importance de la procédure d™essai et les résultats sont discutés à partir des résultats analytiques et des essais de laboratoire disponibles. Ceci est également évalué à la lumière des travaux antérieurs rapportés dans la littérature. 1 0BINTRODUCTION 1.1 8BBackground Retrogressive landslides in sensitive clays are historically known for their ability to cause varying degrees of destruction. Such occurrences often result in large devastating landslides because the involved slide debris can easily be sufficiently remolded to flow out of the slide area, see Figure 1 (e.g., Bishop 1967; Bjerrum 1973; Mitchell and Markell 1974; Lebuis and Rissmann 1979; Tavenas et al. 1983; Thakur et al. 2014a). Therefore, retrogression potential of a landslide must be assessed as a part of the spatial planning for infrastructure developments including road, railroad residential and commercial buildings in Norway. A retrogressive type of landslide occurs on seemingly stable slopes as a result of an initial local slide. In highly sensitive clays, flow slides of large extent usually start with an initial slide of limited extent. For such flow slides to occur after an initial slide, it is important that the slide debris should be sufficiently disintegrated or remolded, followed by a possibility to be able to flow out of the slide area (Tavenas et al. 1983; Thakur and Degago. 2013). There may be additional factors, such as the topography and the initial stability of the area behind the initial slide zone. However, flow slides are less likely to occur if sufficient disintegration of sensitive clay does not takes place. Figure 1. Illustration of flow slides in sensitive clays (Thakur and Degago 2014) 1.2 9BResearch question In the literature, several indicators of potential for flow slides of sensitive clay exist, e.g. the remolded shear strength (cRurR), the liquidity index (IRLR), the sensitivity (SRtR), the quickness (Q). Although these criteria are useful

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