Numerical 3D deterministic models of offshore monopile foundations are computationally-expensive and thus they present a great obstacle to the use of the conventional Monte Carlo Simulation (MCS) methodology for the probabilistic analysis. In this paper, a reliable and efficient Kriging-based probabilistic model called Global Sensitivity Analysis enhanced Surrogate (GSAS) modeling is used. The objective is to perform a probabilistic analysis of a monopile foundation subjected to a combined loading. An undrained normally consolidated clayey soil with spatially varying soil properties was considered. Some probabilistic numerical results are presented and discussed.