Coupled CFD-DEM method for undrained biaxial shear test of methane hydrate bearing sediments

Methane hydrate (MH), a potential source of future energy, is extensively deposited in marine sediments. It is essential to understand the mechanical properties of methane hydrate bearing sediments (MHBS) for applications relevant to mining and geotechnical engineering. This study aims to investigate the undrained shear strength of MHBS through coupled computational fluid dynamics and discrete element method (CFD-DEM) numerical approach. The Tait's fluid state equation is implemented into the Navier-Stokes equation-based CFD, while the DEM is used to model granular particle system of MHBS. The CFD-DEM tool is first verified by two typical geomechanics problems where analytical solutions are available. The simulations show that the stress-strain behavior of MHBS depends on temperature, back pressure and MH saturation, as observed in reported experimental results. The presence of MH alters the hardening response of clean sand into softening response due to the bonding effects of MH. The friction angles and cohesions described by total stress and effective stress both increase as the back pressure and MH saturation increase or the temperature drops. There is significant localization in MH bond breakage events but no localization effect is observed in fluid flow and excess pore pressure distribution. This is because fluid is mostly controlled by the boundary conditions instead of specific fluid-particle interactions locally in the simulated quasi-static loading.