The development in harvesting trend of wind energy is evidenced as a result of the Paris convention. Therefore, future wind turbines tend to move towards deeper water, which sets a requirement of larger capacity support structure. The design guidelines of Gravity Based Foundation (GBF) which is capable of supporting deeper water wind turbines lack attention on the cyclic response of the foundation. The undrained capacity of GBF in terms of failure envelope under combined loading is investigated numerically, in order to shed light on the effect of cyclic loads on the capacity of the foundation. A GBF supporting a 5 MW wind turbine on sandy soil domain is designed based on the static conditions. A critical state model called Hypoplastic sand model with intergranular strain concept is adopted to represent the soil domain in 2D. The influence of factors such as relative density (Dr), load characteristics (¿c yc & ¿avg ) and the wave frequency on the pore pressure behaviour are analysed in the event of concluding a critical case. Moreover, it should be noted that the number of cycle is restricted to 50 cycles as a result of limitations in the implicit method. An undrained failure envelope is developed for the critical case, which in comparison with original envelope reveals the expansion in undrained capacity with respect to the number of cycles. It is inferred that the expansion in the capacity is because of the process known as densification which overcomes the effect of pore pressure on the failure envelope. It is also worth noting that the consolidation phase which is used to model the loads has a significant influence on the expansion of the failure envelope.