Quantifying residual strength in hydrate-bearing sediments under large deformation via a novel high-pressure ring-shear apparatus

To elucidate the failure mechanisms of hydrate-bearing sediments under large-deformation shear and to assess the associated submarine geohazard risks, this study addresses key limitations of existing ring-shear apparatuses, specifically concerning high-pressure sealing and internal temperature monitoring, through significant modifications to a prior design. Enhancements include a demountable inner wall with an interlinked sealing mechanism to improve pressure integrity and an optimized sensor configuration for precise temperature measurement at the shear interface. These innovations have yielded a new high-pressure, low-temperature ring-shear instrument. This apparatus achieves maximum loading capacities of 25 MPa normal stress and 7.5 MPa shear stress, and operates reliably across a broad temperature range (–30 to 180°C) to facilitate in situ hydrate formation and subsequent large-displacement shear testing. Systematic verification confirms stable operation and excellent data reproducibility. Comparative analysis under baseline conditions of 12 MPa pore pressure and 1°C reveals distinct mechanical responses: hydrate-bearing sediments exhibit marked strain-softening behavior, with peak strength increases of 129.5–273.4% and a stable residual strength ratio of 47–70% relative to hydrate-free specimens, which display only strain hardening. This instrument provides an advanced experimental platform and critical technical support for investigating the strength evolution of deep-sea hydrate-bearing strata and for related geohazard risk assessment.