Preferential gas pathway formation in Boom Clay under isotropic stress
Preferential gas pathway formation in Boom Clay under isotropic stress
Deep geological repositories (DGRs) are widely considered the reference solution for the long-term management of high-level radioactive waste. In Belgium and the Netherlands, the plastic Boom Clay is being extensively studied as a potential host rock for geological disposal. As a poorly indurated material exhibiting soft-rock behaviour, Boom Clay provides a particularly relevant framework for investigating gas transport in low-permeability geomaterials. Gas will be mainly generated in the repositories due to the anaerobic corrosion of metallic components and the degradation of organic matter. Thus, gas might progressively accumulate, causing an increase in pore pressure, which will influence the hydro-mechanical response of the host formation [1]. If the pressure build-up is sufficient, gas migration may no longer be governed solely by dissolved-gas diffusion and classical two-phase flow, but instead may evolve towards the development of preferential pathways, especially along bedding-controlled heterogeneities and pre-existing discontinuities [2].
Previous laboratory investigations on Boom Clay, especially under oedometer conditions and supported by microstructural analysis, have already provided valuable evidence of strongly coupled hydro-mechanical behaviour during gas injection, including sample expansion, pathway development along bedding planes, and associated changes in permeability [3]. However, under these test conditions, the sample is subjected to zero radial deformation, which may influence the initiation and development of pressure-dilatant gas pathways, particularly when vertical gas flow is parallel to the bedding plane orientation.
As gas transport in such materials is closely associated with the development of pressure-dilatant preferential pathways, an experimental framework that enables less-constrained, displacement-controlled responses is better suited to investigating the initiation and propagation of these pathways under axial- and radial-stress-controlled conditions.
To better capture this behaviour, an experimental campaign has been launched using an isotropic testing cell developed at the Geotechnical Engineering Laboratory of the Universitat Politècnica de Catalunya (UPC). In this setup, the sample first underwent an isotropic loading stress path to reach effective stress under in situ conditions, and subsequently, was subjected to gas injection to induce the opening of preferential pathways. Unlike in oedometer conditions, the sample was allowed to deform laterally, enabling a more realistic representation of pathway development during gas transport.
Salar Lakimahalleh; Laura Gonzalez-Blanco; Enrique Romero
International Conference on Advances and Innovations in Soft Soil Engineering (ICAISSE2026)
Multiphysics Behaviour
https://doi.org/10.53243/ICAISSE2026-224