The fixed gravity-based structure (GBS) platform has been widely constructed offshore in support of exploring and drilling activities for oil and gas industry. The aim of the present study is to investigate the wave-induced instantaneous liquefaction of a poro-elastic seabed around a GBS offshore platform, including the consideration of the effect from the platform deck. Our approach is using an integrated three-dimensional numerical model that developed based on the Finite Volume method (FVM) in OpenFOAM. In addition, a protection system for the GBS platform has been proposed and its effect on the prevention of the wave-induced momentary liquefaction have been demonstrated. A series of simulations are performed, including a consolidation process, the fluid–structure–seabed interactions and the wave-induced liquefaction and shear failure near the GBS. Numerical results reveal that the proposed protection system can significantly reduce the wave forces and the liquefaction depth in front of the platform. The parametric study reveals that the wave height and current velocity have significant impact on the seabed liquefaction in the vicinity of the GBS offshore platform. The protecting effect of the protection piles decreases with increasing of the column spacing and the distance from the GBS.