A shipborne triaxial testing system for quasi-in-situ mechanical characterization of gas hydrate-bearing deep-sea sediments

Accurate mechanical characterization of gas hydrate-bearing deep-sea sediments is crucial for the safe and efficient exploitation of subsea energy resources. To overcome the inherent sample disturbance in traditional methods, a novel shipborne triaxial testing system was developed to enable quasi-in-situ mechanical evaluation of fragile hydrate-bearing cores. The apparatus integrates an automated, non-contact transfer mechanism and a high-fidelity environmental simulation module, accurately reproducing deep-sea conditions up to 30 MPa (±10 kPa) and 4 °C (±0.1 °C). Functional validations demonstrate excellent sealing performance with a pressure decay rate below 0.05 MPa/h and a near-zero disturbance transfer speed of <1 mm/s. Comparative tests demonstrate that the system constrains measurement errors to 3.7% for deviatoric stress and 2.8% for pore pressure compared to standard laboratory devices. In-situ simulation trials using authentic hydrate-bearing sediment cores from the South China Sea under 15 MPa back pressure successfully yielded geomechanical parameters (cohesion c = 3.14 kPa, internal friction angle φ = 1.72°). These quantitative results confirm the system's capability to capture the authentic low-strength, high-compressibility behaviors of natural hydrate reservoirs, providing robust mechanical data and technical support for geohazard risk assessment and resource development in subsea environments.