A Novel High-Pressure and Low-Temperature Ring Shear Apparatus for Large-Scale Deformation of Hydrate-Bearing Sediment

Metastable natural gas hydrates in shallow deep-sea sediments significantly impact submarine slope stability and resource extraction safety. Elucidating the large-deformation shear failure mechanisms of hydrate-bearing sediment is crucial for early warning of marine geohazards. This study describes the successful development of a novel high-pressure (24.98 MPa) and low-temperature (−30 °C) ring-shear apparatus specifically designed for hydrate-bearing sediment, developed for the first time. Key technical solutions effectively solved critical challenges, including dynamic sealing under combined high-pressure, low-temperature, and large-deformation shear conditions, precise wide-range temperature control without interfering with the specimen interface, and reliable large-deformation shear load transfer. The apparatus enables in situ hydrate formation under simulated deep-sea conditions, precise pore pressure control, and real-time monitoring throughout the entire shearing process. Validation experiments confirmed its excellent repeatability, with the coefficient of variation for both peak and residual shear stresses of hydrate-bearing sediment below 4%. Significantly, comparative studies revealed a fundamental alteration in sediment mechanical behavior induced by hydrates: hydrate-bearing specimens exhibited distinct strain-softening characteristics, whereas hydrate-free specimens showed strain-hardening behavior. This novel apparatus overcomes the limitations of existing equipment, providing critical and irreplaceable technical support for quantifying landslide risks in hydrate-bearing strata.