Experimental Study on Failure Mechanism of Clay Seabed Induced by Gas Migration

Shallow gas in marine clay sediments poses significant geohazards to offshore infrastructure, yet predictive frameworks linking sediment properties to seabed failure patterns remain inadequate. Through quasi-2D gas injection experiments with centrifuge-consolidated clay achieving field-representative strength profiles, this study reveals gas migration behavior governed by soil strength, water depth, and pre-existing defect presence. Three distinct migration modes are identified: (1) discrete bubble migration in low-strength sediments under shallow water conditions, (2) stable cavity formation in high-strength sediments with comparable hydraulic conditions, and (3) conduit-dominated pipe flow under deep water environments regardless of sediment strength. Cavity formation induces the most substantial seabed deformation, while pipe flow causes minimal disturbance. Gas invasion alone cannot initiate soil fractures in clay seabeds, but buoyancy-driven gas migration displaces water into overlying sediments, potentially inducing hydraulic fracturing when pre-existing defects are present. These defects reduce the deforming region dimension by over 80% by creating stable fracture pathways, while preserving the fundamental migration modes. Finally, a phase diagram is established, highlighting shallow-water, high-strength sediment zones as having the highest geohazard potential.