Experimental study of mechanical properties of deep-sea hydrate-bearing sediments under multi-field coupling conditions

To ensure the long-term safety of hydrate-bearing sediments (HBSs) in the deep sea, it is necessary to conduct a comprehensive study of the mechanical properties of HBSs, which is closely related to the safe extraction of natural gas hydrates (NGH). In this study, a HBSs preparation method was proposed preparing HBSs artificially to meet the test requirement. A series of triaxial shear tests were carried out by the self-developed HBSs multi-field coupling intelligent triaxial test device to analyze the effects of different hydrate saturation and NaCl concentration on the mechanical properties of HBSs. The results show that HBSs have elastic-plastic properties under multi-field coupling conditions, and the stress-strain curves show a strain-hardening trend. Hydrate saturation affects the shear strength of hydrate-bearing sediment critically. When the hydrate saturation is S h >35 %, the cohesion and internal friction angle is directly proportional to the hydrate saturation. When the NaCl concentration is low, the cohesion of HBSs is more affected by the NaCl concentration, and the shear strength and yield strength are proportional to NaCl concentration. When NaCl concentration is high, the internal friction angle of HBSs is more affected by NaCl concentration and the shear strength is inversely proportional to NaCl concentration. Under the condition of multi-field coupling, the influence of each factor on the mechanical properties of HBSs has an upper limit, which is not a purely linear relationship. • Hydrate saturation affects the shear strength of hydrate-bearing sediment critically. • Cohesion and internal friction angle are directly proportional to hydrate saturation. • NaCl has an important effect on cohesion in hydrate-bearing sediment. • NaCl affects the internal friction angle of hydrate-bearing sediment accordingly.