DEM simulation of grain-coating type methane hydrate bearing sediments along various stress paths

Abstract

This study explores the mechanical behaviors of grain-coating type methane hydrate bearing sediments (MHBS) using the discrete element method (DEM) under four typical compression conditions, i.e. triaxial, isotropic, constant stress ratio, and true triaxial. The particle-scale mechanism of grain-coating type MHBS is taken into account in the DEM contact model. The numerical results show that MH saturation and bond result in increased structural yield stress. The mean stress and volumetric change are larger under lower stress ratio in the constant stress ratio compression tests. The yield envelop obtained from the true triaxial compression test agrees well with the Lade-Duncan criterion. The shear strain contours in deviatoric plane can be described by changing the size of Lade-Duncan yield surface. Grain-coating type MHBS behaves like weakly-bonded sand, as cohesive MH bonds break at the very early stage of loading. Upon loading, the frictional properties of MH host sands evolve according to the change in grain morphology (i.e., particle enlargement and angulation). The simulation results and revealed particle-scale mechanism are useful in future development of constitutive models for MHBS.