Experimental Investigation on Effects of Buoyancy Loading Rate on Pullout Resistance of Composite Suction Caissons in Subsea Hydrogen Storage

Underwater compressed hydrogen storage is poised to become a promising enabler for harnessing intermittent offshore renewable energy. The substantial buoyancy generated by the density difference between hydrogen and seawater presents significant anchoring challenges for seabed foundations. This study introduces a novel composite suction caisson (CSC) foundation integrated with compressed hydrogen accumulators and investigates its anti-uplift mechanisms under operational buoyancy variations. Scaled physical modeling tests are conducted with controlled buoyancy loading rates ranging from 1 to 100 N/s, representing realistic gas injection scenarios. Comparative analyses of pullout resistance among regular suction caissons (RSCs), modified suction caissons (MSCs), and CSCs reveal that the proposed CSC configuration enhances bearing capacity by 8.4%–57.8% across the tested loading rates. Transient pore pressure responses are synchronously monitored. The results demonstrate that the suction force consistently contributes a high proportion of the total resistance, ranging from 55% to 94%. A practical peak pullout load for suction caisson foundations is proposed as a criterion for defining pullout failure. A dimensionless prediction model for this practical peak pullout load is developed, exhibiting an average prediction deviation of 7.9% for the CSC.