Scale Effect on Shear Behavior of Loose Sand in Triaxial Testing and its Implication in Engineering Design and Analysis

Tarek Omar, Abouzar Sadrekarimi

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Soil Mechanics

ABSTRACT: ct on Shear Behavior of Loose Sand in Triaxial Testing and its Implication in Engineering Design and Analysis Tarek Omar and Abouzar Sadrekarimi Department of Civil and Environmental Engineering, Western University, London, Ontario, Canada ABSTRACT The influence of sample size on the shear behavior of loose sand is presented. Several drained and undrained static triaxial compression shear tests are performed on three different specimen sizes of the same sand. The test results indicate that the behavior of loose sand is strongly influenced by the specimen size, with larger specimens exhibiting a stiffer behavior during isotropic compression, and mobilizing smaller shear strengths and effective friction angles. The measured critical state parameters and shear strengths are employed to investigate scale effects in engineering design and analysis. The results show that all analyses are significantly affected by the strength parameters of the same soil determined from different specimen sizes. Accordingly, the choice of a representative sample size could have a profound impact on the safety or cost effectiveness of engineering analysis and design. RÉSUMÉ L'influence de la taille de l'échantillon sur le comportement en cisaillement sable lâche est présentée. Réalisés en compression triaxiale statique, plusieurs essais en cisaillement drainé et non drainé ont été effectués sur trois différentes tailles de spécimens du même sable. Les résultats des essais indiquent que le comportement du sable lâche est fortement influencé par la taille du spécimen, les plus gros de ceux-ci présentant un comportement plus raide durant la compression isotrope et mobilisant de plus petites forces de cisaillement et des angles de friction effectifs moindres. Les paramètres d'état critique et les résistances au cisaillement mesurés pévaluer les effets d'échelle liés à la conception et à l'analyse. Les résultats montrent que toutes les analyses sont influencées de manière significative par les paramètres de résistance déterminés sur le même sol à partir de différentes tailles de spécimens. En conséquence, le choix de la taille d'un échantillon représentatif pourrait avoir de profondes répercussions sur la sécurité ou sur de l'ingénierie et de la conception. 1 INTRODUCTION Different studies employ different specimen diameters (D) and heights (H) in triaxial compression tests. The behavior of a particular soil from different studies are often compared without due attention to the differences in specimen size and its effect on soil shear behavior. For example, Table 1 presents a summary of the different specimen sizes used in different triaxial testing studies of sand behavior. Table 1. Summary of specimen sizes used in past studies. size (mm) Sand Researcher D H 38 NP1 Leighton Buzzard Scott (1987) 50 100 Unimin Garga (1988) 51 102 Ottawa/Mississippi Sadrekarimi (2011) 71 150 Ottawa Frost (2000) 74 150 Monterey Ladd (1978) 75 NP1 Banding Castro (1969) 76 150 Erkask Been et al. (1991) 100 NP1 Leighton Buzzard Scott (1987) 100 200 Loire river Hu et al. (2010) 102 200 Silty sand Yamamuro (1997) 250 500 Loire river Hu et al. (2010) 300 675 Ticino 9 Jefferies et al. (1990) 300 600 Granular material Seif el Dine. (2009) 1000 1500 Loire river Hu et al. (2010) 1 NP: not provided Several researchers have studied the effect of sample size on the behavior of cohesionless soils using triaxial shear tests (Marsal 1967; Scott 1987; Been et al.1991; Hu et al. 2010). For example, Scott (1987) performed drained triaxial compression tests on dense Leighton Buzzard sand specimens of diameters 38 mm and 100 mm and found a higher peak strength and initial shear modulus in the larger specimen whereas smaller post peak shear strength was mobilized in the larger specimen. Jefferies et al. (1990) investigated the influence of sample size on the drained shearing behavior of Ticino 9 sand specimens of diameters 35, 75, 150, and 300 mm. They found that the smaller specimen exhibits the greatest volumetric strain despite its smallest peak deviator stress. Hu et al. (2010) developed a set of drained triaxial compression tests on various sizes of Loire River sand and found that the pre-peak behavior was not affected by the specimen size, whereas the post-peak behavior mobilized smaller friction angle. Similar results have been documented by many other studies on the effect of shear box size on the results of direct shear tests (Cerato and Lutenegger 2006; Wu et al. 2007; Bareither et al. 2008). Some other investigators have compared the behavior of granular materials with different ranges of particle sizes as an alternative approach for studying specimen scale effect (Tatsuoka 1997; Oie et al. 2003; Farbodfar 2013). For example, Fabodfar (2013) performed series of direct shear tests on

RÉSUMÉ: Effect on Shear Behavior of Loose Sand in Triaxial Testing and its Implication in Engineering Design and Analysis Tarek Omar and Abouzar Sadrekarimi Department of Civil and Environmental Engineering, Western University, London, Ontario, Canada ABSTRACT The influence of sample size on the shear behavior of loose sand is presented. Several drained and undrained static triaxial compression shear tests are performed on three different specimen sizes of the same sand. The test results indicate that the behavior of loose sand is strongly influenced by the specimen size, with larger specimens exhibiting a stiffer behavior during isotropic compression, and mobilizing smaller shear strengths and effective friction angles. The measured critical state parameters and shear strengths are employed to investigate scale effects in engineering design and analysis. The results show that all analyses are significantly affected by the strength parameters of the same soil determined from different specimen sizes. Accordingly, the choice of a representative sample size could have a profound impact on the safety or cost effectiveness of engineering analysis and design. RÉSUMÉ L'influence de la taille de l'échantillon sur le comportement en cisaillement

Access this article:
Canadian Geotechnical Society members can access to this article, along with all other Canadian Geotechnical Conference proceedings, in the Member Area. Conference proceedings are also available in many libraries.

Cite this article:
Tarek Omar; Abouzar Sadrekarimi (2014) Scale Effect on Shear Behavior of Loose Sand in Triaxial Testing and its Implication in Engineering Design and Analysis in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper119,author = Tarek Omar; Abouzar Sadrekarimi,title = Scale Effect on Shear Behavior of Loose Sand in Triaxial Testing and its Implication in Engineering Design and Analysis ,year = 2014}