A novel high-pressure low-temperature interface shear apparatus: Mechanical behavior of interface between hydrate-bearing sediment and foundation structure

Metastable hydrates are widely distributed in shallow deep-sea sediments, posing significant risks to the long-term stability of offshore foundation structures. Unveiling the weakening mechanisms at the hydrate-bearing sediment–structure interface is crucial for establishing a theoretical framework for the safe design of deep-sea structures. A high-pressure (up to 12.5 MPa), low-temperature (down to −30 °C) interface shear test apparatus suitable for investigating the hydrate-bearing sediment–structure interface has been designed for the first time. The key innovations of this system include the dynamic sealing and precise regulation of interface temperature and pore pressure. This apparatus enables in situ hydrate generation under simulated deep-sea conditions, precise pore pressure regulation, and real-time monitoring of shear behavior. Verification experiments demonstrate excellent repeatability, with variations in peak and residual shear stresses at the hydrate-bearing sediment–steel interface remaining below 5%. Comparative tests reveal distinct mechanical responses: the hydrate-bearing interface exhibits strain-softening behavior, whereas the hydrate-free interface shows strain-hardening characteristics. This apparatus addresses the limitations of existing systems and provides a foundational structure for precise measurement and comprehensive analysis of the mechanical properties.