Modelling the freezing and thawing behaviour of saturated soils

This thesis presents an investigation of the thermo / hydro / mechanical behaviour of saturated soils with cryogenic suction effects. The flow relationships accommodate a number of mechanisms: i) heat transfer by conduction, convection, and latent heat transfer and ii) moisture transfer in the liquid phase due to pressure head, elevation head, and thermal gradients. The mechanical behaviour of the soil is modelled by an elasto-plastic work hardening modified Cam- Clay constitutive model. A numerical solution for the theoretical formulation is presented. Standard finite element methods are used for spatial discretisation and finite difference methods are used for temporal discretisation. Verification of the model is achieved by means of programme of tests to check the following cryogenic components i) coupled thermo-hydraulic response, ii) deformation behaviour of the fully coupled thermo-hydro-mechanical model, iii) transient coupled liquid flow and deformation behaviour, and iv) latent heat of fusion. Validation focused on the impact of the cryogenic related processes included within the proposed theoretical formulation. In particular the development of ice lenses and the movement of moisture under cryogenic suction were investigated. The performance of the proposed model with respect to a number of variables was subsequently explored in order to determine their effect on the magnitude and growth of ice lenses in a freezing soil. The model was then applied to a large scale freezing experiment, namely a fully coupled thermo / hydro / mechanical simulation. The simulated results show a good correlation with the experimental results by predicting the patterns and trends of experimentally observed behaviour and the cryogenic processes that occur during the freezing and thawing of frost susceptible soils. It was therefore concluded that the proposed model is capable of providing a good representation of the fully coupled THM behaviour of saturated soils with cryogenic effects