The activities associated with the numerical modeling are centered on the extension of the fully coupled THMC finite element (FE) 3D program CODE_BRIGHT to deal with discontinuities and interfaces in geological materials. This code is based on a multiphase/multispecies mathematical formulation that consists of three main set of equations:

• balance equations (i.e. momentum balance, balance of internal energy, and mass balance of species: water, air, solid and chemical species);
• constitutive equations (e.g. Darcy’s and Fourier’s laws, retention curve, stress-strain relationship), and
• equilibrium restrictions (e.g. physcormetric law and Henry’s law, to account for dissolve gas in liquid).

This in-house program was developed to conduct coupled THCM analysis in ‘continuous’ geological media, and therefore is not well-suited to tackle problems involving ‘discontinuities and interfaces’. The mesh fragmentation technique (MFT) has been adopted to extend this program to deal with discontinuities. The MFT (Sanchez et al., 2014) has been recently proposed and applied with success to simulate the formation and propagation of drying cracks in soils. The MFT uses solid FEs with high aspect ratio to describe the crack formation process in an initially continuous medium.

The MFT has a number of advantages, e.g.: i) problems with discontinuities can be modeled entirely in a continuum framework using standard 2D or 3D finite elements typically available FE codes; ii) high aspect ratio elements require neither discrete constitutive relations nor special integration rules to obtain the internal forces; and iii) it is relatively straightforward to implement the MFT in a standard FE program.

The figures below shows recent results related to the numerical modeling of a gas breakthrough experiments through a clay barrier material using the numerical tool that is being upgraded in this project.