A thermo-hydro-mechanical model for multiphase geomaterials in dynamics with application to strain localization simulation

What is it about?

In this paper, the non-isothermal elasto-plastic behaviour of multiphase geomaterials in dynamics is investigated with a thermo-hydro-mechanical model of porous media. The supporting mathematical model is based on averaging procedures within the hybrid mixture theory. A computationally efficient reduced formulation of the macroscopic balance equations that neglects the relative acceleration of the fluids, and the convective terms is adopted. The modified effective stress state is limited by the Drucker–Prager yield surface. Small strains and dynamic loading conditions are assumed. The standard Galerkin procedure of the finite element method is applied to discretize the governing equations in space, while the generalized Newmark scheme is used for the time discretization. The final non-linear set of equations is solved by the Newton method with a monolithic approach. Coupled dynamic analyses of strain localization in globally undrained samples of dense and medium dense sands are presented as examples. Vapour pressure below the saturation water pressure (cavitation) develops at localization in case of dense sands, as experimentally observed. A numerical study of the regularization properties of the finite element model is shown and discussed. A non-isothermal case of incipient strain localization induced by temperature increase where evaporation takes place is also analysed.

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Why is it important?

For many engineering problems, such as earthquake engineering, environmental geomechanics, interface problems in soil mechanics, biomechanics and seismic wave scattering, the analysis of the dynamic response of multiphase porous media is important. Further, there are also situations where the additional effect of temperature has to be considered. This is the case for instance of catastrophic landslides, where the mechanical energy dissipated in heat inside the slip zone may lead to evaporation of the pore water, creating a cushion of zero friction which may accelerate the movement of the landslide (e.g. [1, 2]). Another interesting case is the seismic analysis of deep nuclear waste disposals where temperature increments linked to the failure of canisters could create localized failure zones acting as preferential escape zones for the fluids containing radionuclides.