Abstract
Poisson’s ratio is typically assumed to be constant for both saturated and unsaturated soils. However, the back-calculated Poisson’s ratio using the relationship between elastic and shear modulus (i.e. the equation for homogeneous, isotropic and linear elastic continuum) published in the literature showed that the Poisson’s ratio is not constant but decreases with the degree of saturation (or increasing suction). In the present study, more focused investigations are undertaken to study the influence of Poisson’s ratio on the stress vs. settlement (SVS) behaviour of shallow foundations in an unsaturated fine-grained (UFG) soil. The FEA are carried out using the software, SIGMA/W (GeoStudio 2007) to better understand the SVS behavior taking account of the influence of Poisson’s ratio for different matric suction values and compared with the model footing tests conducted in an UFG soil. Several suggestions are made with respect to the influence of Poisson’s ratio on the SVS behavior of shallow foundations in the UFG soils based on the results of this study.
Highlights
In recent years, significant advancements were made in the area of geotechnical engineering applications extending the mechanics of unsaturated soils for the shallow foundations (Ausilio & Conte 1999, Costa et al, 2003, Cerato & Lutenegger 2006, Oh & Vanapalli 2013a), deep foundations (Weaver & Grandi 2009, Vanapalli & Taylan 2012), and heave analysis (Chao et al, 2001), etc
More and more studies on the unsaturated soils are directed to Finite Element Analysis, which can be attributed to the recent advancements with respect to several semi-empirical or constitutive models for unsaturated soils (Georgiadis et al, 2003, Vu & Fredlund 2006, Wejrungsikul et al, 2011, Oh & Vanapalli 2011a,b, Adem & Vanapalli 2013, Gallipoli et al, 2013)
An attempt is made to estimate the stress vs. settlement behavior of a model footing in unsaturated fine-grained soils using the Finite Element Analysis (FEA) extending mechanics of unsaturated soils
Summary
Significant advancements were made in the area of geotechnical engineering applications extending the mechanics of unsaturated soils for the shallow foundations (Ausilio & Conte 1999, Costa et al, 2003, Cerato & Lutenegger 2006, Oh & Vanapalli 2013a), deep foundations (Weaver & Grandi 2009, Vanapalli & Taylan 2012), and heave analysis (Chao et al, 2001), etc. Mohamed & Vanapalli (2006) carried out model footing (B x L = 100 mm x 100 mm and 150 mm x 150 mm) tests in a sandy soil for four different average matric suction values (i.e. 0, 2, 4 and 6 kPa) Based on their experimental results, Vanapalli & Mohamed (2007) proposed a semi-empirical model to estimate the variation of bearing capacity of coarse-grained soils with respect to matric suction. The studies by Oh & Vanapalli (2011b, 2012) show that the SVS behaviour of shallow foundation in unsaturated soils can be reliably estimated when the FEA is carried out using the elastic modulus function (i.e. variation of elastic modulus with respect to the matric suction) This is because the FEA based on elastic - perfectly plastic model is mainly influenced by the elastic modulus and the Poisson’s ratio, n. The bearing capacity values were determined using a graphical method (i.e. stress corresponding to the intersection of elastic and plastic line on the SVS behavior)
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