Microstructurally Related Model for Predicting Behavior of Unsaturated Soils with Double Porosity in Triaxial Space

Abstract

Microstructure can have an important impact on the hydraulic and mechanical behaviour of unsaturated soil and so it is necessary for it to be considered in constitutive models to enable accurate predictions of soil behaviour. This paper focuses on constitutive modelling of soils exhibiting a dual-porosity structure. Based on the assumption that macro and micropores contained in the double porosity structure have different influences on the mechanical and hydraulic behaviour, the effective degree of saturation was selected as a microstructural index. This microstructural index was implemented within a Bishop's effective stress based approach and the Glasgow Coupled Model and the Modified Camclay Model were adopted as the basic framework for the development of a constitutive model. Typical samples of low-expansive, nonexpansive and collapsible soils with dual porosity were selected to validate the model's performance, with the model found to perform well when compared with experimental data in terms of isotropic compression, triaxial shear and wetting tests.

Consideration of microstructure in modelling the hydro-mechanical behaviour of unsaturated soils

“…The establishment of the new model presented in ( [25]), which considers the microstructure, is based on the widely used Glasgow Coupled Model (GCM) ( [25][26][27]). The non-microstructure-dependent GCM has been modified to develop a microstructure-related model by replacing the degree of saturation by the effective degree of saturation.…”

“…where 𝜎 𝑖𝑗 is the total stress tensor; 𝑢 w is the water pressure; 𝑢 a is the air pressure; 𝛿 𝑖𝑗 is the Kronecker delta. The basic framework of the microstructure-related model is defined below ( [25][26][27]).…”

“…However, both the models underestimated the deviator stress at all axial strains. This is a common issue that originates from the deficiency of the Modified Cam-Clay Model ( [25,27]) upon which both the models are based.…”

“…( [25]) have reported a microstructure-related model. The model was validated by considering various soil types under different loading conditions.…”