Gas transport in granular compacted bentonite: coupled hydro-mechanical interactions and microstructural features

¹ Geomechanics Group, International Center for Numerical Methods in Engineering, Gran Capità s/n 08034, Barcelona, Spain
² Department of Civil and Environmental Engineering, Universitat Politècnica de Catalunya, Jordi Girona 1-3, 08034, Barcelona, Spain
³ Nationale Genossenschaft für die Lagerung radioaktiver Abfälle (NAGRA), Wettingen, Switzerland

^* Corresponding author: laura.gonzalez.blanco@upc.edu

Abstract

The initial conditions (dry density and saturation state), the stress state and its history, and the deformation undergone during gas migration, affect the gas transport processes in granular compacted bentonite. Additionally, the sample microstructure set on compaction has a significant influence since gas tends to flow through preferential pathways. This experimental study intends to shed light on the gas transport and their coupled hydro-mechanical interactions with particular emphasis in the changes of the pore and pathway network. Controlled volume-rate gas injection followed by shut-off and dissipation stages have been performed under oedometer conditions. The microstructure of the samples has been characterised with three different techniques before and after the gas injection tests: Mercury Intrusion Porosimetry (MIP), Field-Emission Scanning Electron Microscopy (FESEM) and X-ray Micro-Computed Tomography (μ-CT). The results show a coupling of the deformational behaviour during the gas flow, revealing an expansion of the samples upon the development of gas pathways, which have been detected with the microstructural techniques. The opening of these pressure-dependent and connected pathways plays a major role in gas migration.