Discrete-element numerical modelling method for studying mechanical response of methane-hydrate-bearing specimens

It is important to understand the deformation mechanism of methane-hydrate specimens (MHSs) to avoid deforming the seabed during methane-hydrate production. For this purpose, discrete-element method (DEM) modelling is advantageous because it requires much less cost and effort compared to artificial specimens and in situ sediments. In this study, a method for generating DEM numerical simulation models of MHSs is proposed to study the deformation mechanism of MHSs. First, numerical models that consider the saturation of methane hydrate (S-MH), following which the bi-axial compression of these models is simulated. The mechanisms controlling the shear strength of MHSs are verified and modified by investigating the stress-strain response behavior, crack-development process, and evolution of the void change rate (E-change) of MHSs. The increases of the peak strength and secant elastic modulus of the MHS with the increment of confining pressure follow parabolic relationships. Under different loading rates, the peak strength tends to increase parabolically with the increment of loading rate, while the relationship between the secant elastic modulus and loading rate is linear. Based on the testing results, empirical formulas of peak stress and elastic modulus are proposed for different confining-pressure and strain-rate conditions.