Experimental study of Leda clay-steel interface shear behaviour

Ahmed Taha, Mamadou Fall

Dans les comptes rendus d’articles de la conférence: GEO2010 Calgary: 63rd Canadian Geotechnical Conference & 6th Canadian Permafrost Conference

Session: W1-A

ABSTRACT: Understanding the interface shear behaviour between Leda clay and structure is significantly important for the design and stability analysis of many geotechnical structures (e.g., friction piles, retaining walls, and earth reinforcement). In this study, direct shear tests have been conducted to investigate the shear behaviour of the interface between Leda clay and steel material. All tests are carried out with a standard direct shear test apparatus at normal stresses which range from 250 to 450 kPa. Furthermore, the effects of several parameters (e.g., steel surface roughness, overconsolidation ratio (OCR) of the Leda clay, and saturation degree) on the interface shear behaviour are also studied. Valuable results have been obtained with regard to the interface behaviour of Leda clay. The results presented in this paper can be useful for geotechnical design on Leda clay. . RESUMÉ La compréhension du comportement au cisaillement de l'interface entre une argile Leda et une structure est essentielle pour la conception et l'analyse de plusieurs ouvrages de géotechnique (pieux à frottement, murs de soutènement, terre-armée, etc.). Dans cette recherche, des essais de cisaillement rectiligne ont été conduits pour étudier le comportement mécanique de l'interface argile Leda/matériel d'acier. Tous les tests ont été effectués avec un appareil de cisaillement rectiligne standard. Les pressions normales appliquées varient entre 250 à 450 kPa. En plus, les effets de plusieurs paramètres (rugosité de la surface de l'acier, degré de surconsolidation de l'argile Leda, degré de saturation, etc.) sur le comportement de l'interface ont été aussi étudiés. D'importants résultats ont été obtenus. Les résultats présentés dans cet article peuvent être utiles pour la conception d'ouvrages de géotechnique sur l'argile Leda. 1 INTRODUCTION Thick deposits of Leda clay cover large areas of the provinces of Quebec and Ontario. The existence of Leda clays in these areas has made infrastructure expansion challenging for geotechnical engineers. As the aforementioned areas are fairly heavily populated and industrialized, the importance and behaviour of Leda clays as a foundation soil has led to several investigations of their geotechnical properties (e.g., Crawford 1963, Leroueil 1999). At the locations where Leda clays exist, many foundation engineers have adopted the use of pile foundations as subsurface supporting (heavy) structures to ensure the safe transmission of loading deep into a harder stratum (e.g., moraine, rock). Long end bearing piles, driven through the Leda clay to the deep underlying harder stratum, are often used when heavy loads must be supported (Roy et al. 1981). In many cases, short friction piles in the clay would provide much less expensive foundation solutions. However, their use has been relatively limited despite their lower cost (Roy et al. 1981). This is mainly due to the many unknown aspects of their geotechnical behaviour in the Leda clays. In particular, the interface shear behaviour between pile materials (steel, concrete, and wood) and Leda clay is not sufficiently known. To design reliable and cost-effective pile foundation structures (especially friction piles), it is crucial to understand the mechanical behaviour at the interface pile-Leda clay. This is especially true with regard to interface strength properties used in stability analyses. Several studies have been conducted to understand the interface shear behaviour between pile construction material and cohesionless soils (e.g., Yoshimi and Kishida 1981; Evgin and Fakharian 1996) and the factors that affect the interface shear behaviour. Compared to the large number of research carried out to study the interface behaviour of granular soils, only a few researchers (e.g., Tsubakihara et al. 1993, Tsubakihara and Kishada 1993, Zimnik et al. 2000; Hammoud and Boumekik 2006, Tan et al. 2008, Tariq and Gerald 2009) have conducted studies on the shear behaviour of the interface between cohesive soils and structure. Previous research findings have significantly contributed to a better understanding of the interface shear behaviour of soil-structure. They reveal that the surface roughness, water content, soil composition and structure, and the intensity of the normal load have significant influence on the interface shear behaviour. However, since Leda clay is a special type of soil and different from 'normal' cohesive soils, the results of the aforementioned studies cannot be directly applied to a Leda clay-structure interface. Thus, there is the need to gain knowledge about the interface shear behaviour of Leda clay-structures for a safe and cost-effective design of pile foundations on these soils. Moreover, this understanding is not only important for pile design, but also crucial for the cost-effective design and accurate performance predictions of other relevant civil engineering structures (e.g., retaining walls, reinforced earth, and shallow foundation buried structures (e.g. lined tunnels)). However, no studies have addressed the interface shear behaviour between Leda clay and structure. 27

RÉSUMÉ: ental study of Leda clay-steel interface shear behaviour

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