Exploiting methane hydrate induces deformation and damage to the reservoir

leading to a series of geotechnical engineering problems. Therefore

to achieve safe and effective extraction of hydrates

it is necessary to research the shear deformation characteristics of methane hydrate-bearing sediments(MHBS). The thermo-hydro-mechanical-chemical (THMC) microscopic contact model was utilized to account for hydrate cementation effects and their sensitivity to environmental temperature and pressure. In addition

the flexible boundary was applied to triaxial numerical tests to ensure the full evolution of shear bands. The microscopic mechanism of onset and development of shear bands was studied by considering macro and micro variables such as strain localization

porosity

average pure rotation rate (APR)

bond failure

and spatial distribution of shear band. The results indicate that the flexible boundary used in the triaxial shear test effectively represents the stress-strain and volumetric response of MHBS while ensuring the free deformation of the sample. The shear band has already begun to germinate and to develop during the initial strain hardening stage and becomes more pronounced once it reaches the strain softening stage. Considerable disparities exist in macro- and microscopic parameters

including particle rotation and porosity alterations

both within and outside the shear band. Furthermore

hydrate cementation exerts a dual impact on its host sand. On the one hand

it enhances its strength characteristics

and on the other hand

as a weak link in the shear process

it takes the lead in failure

thus contributing to the emergence of shear bands. The research results have reference value for understanding the mesoscale evolution mechanism of MHBS deformation.