Abstract
Although the deformation of unsaturated soils has usually been described based on simple infinitesimal theory, simulation methods based on the rational framework of finite strain theory are attracting attention especially when solving geotechnical problems such as slope failure induced by heavy rain in which large a deformation is expected. The purpose of this study is to reformulate an existing constitutive model for unsaturated soils (Kikumoto et al., 2010) on the basis of finite strain theory. The proposed model is based on a critical state soil model, modified Cam-clay, implementing a hyperelastic model and a bilogarithmic lnv -lnP ’ (v , specific volume; P ’, effective mean Kirchhoff stress) relation for a finite strain. The model is incorporated with a soil water characteristic curve based on the van Genuchten model (1990) modified to be able to consider the effect of deformation of solid matrices. The key points of this model in describing the characteristics of unsaturated soils are as follows: (1) the movement of the normal consolidation line in lnv -lnP ’ resulted from the degree of saturation (Q , deviatoric Kirchhoff stress), and (2) the effect of specific volume on a water retention curve. Applicability of the model is shown through element simulations of compaction and successive soaking behavior.
Highlights
IntroductionThe stress-strain relationship of unsaturated soils has usually been described based on simple infinitesimal theory, application of the framework of finite strain theory to unsaturated soil mechanics is attracting attention (e.g. [1, 2]), especially when predicting geotechnical issues in which large deformation of the ground (such as a failure of slope or embankment owing to heavy rain or earthquake) is expected
The stress-strain relationship of unsaturated soils has usually been described based on simple infinitesimal theory, application of the framework of finite strain theory to unsaturated soil mechanics is attracting attention (e.g. [1, 2]), especially when predicting geotechnical issues in which large deformation of the ground is expected
We present an outline of a constitutive model for unsaturated soils based on finite strain theory
Summary
The stress-strain relationship of unsaturated soils has usually been described based on simple infinitesimal theory, application of the framework of finite strain theory to unsaturated soil mechanics is attracting attention (e.g. [1, 2]), especially when predicting geotechnical issues in which large deformation of the ground (such as a failure of slope or embankment owing to heavy rain or earthquake) is expected. The constitutive framework of finite strain elastoplasticity has been developed [3,4,5,6] based on the multiplicative decomposition of the deformation gradient [7]. Borja and Tamagnini [8] developed the infinitesimal version of the modified Cam-Clay model for finite strain theory based on a multiplicative decomposition of the deformation gradient ( F Fe Fp ). In their formulation, a yield function is defined as a function of the mean Kirchhoff stress (P) and deviatoric Kirchhoff stress (Q) instead of mean Cauchy stress (p) and deviatoric Cauchy stress (q), respectively. The applicability of the model is discussed through element simulations of compaction and the soaking behavior of unsaturated soils
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