Offshore　wind　turbines　(OWTs)　are　subjected　to　prolonged　external　loading,　including　loads　induced　by　wave　action.　The　soil　undergoes　bi-directional　coupled　shear,　due　to　this　low-frequency　and　long-duration　loading,　the　cumulative　deformation　of　the　offshore　foundation　is　observed　to　increase,　which　poses　a　threat　to　the　functional　reliability　of　the　offshore　wind　turbines.　The　soil　around　the　piles　is　distributed　with　clay　layers.　Due　to　the　complex　mechanical　properties　of　clay,　bi-directional　cyclic　loading　tests　are　performed　to　research　the　drainageinduced　deformation　characteristics　of　clays　in　this　paper.　Based　on　these　test　results,　the　variation　of　hysteresis　loops　of　stress-strain,　resilient　modulus,　and　the　cumulative　strain　are　found　to　exhibit　a　strong　correlation　with　both　the　cyclic　stress　level　and　the　confining　pressure.　The　stress-strain　hysteresis　loops　and　resilient　modulus　have　significantly　different　trends　at　higher　or　lower　cyclic　stress　levels.　Then　an　empirical　model　that　uniformly　reflects　the　strain-hardening　and　softening　characteristics,　and　an　empirical　model　reflects　the　characteristics　of　cumulative　strain　development　in　soils　is　established.　Finally,　the　performance　of　the　permanent　cumulative　strain　prediction　model　is　assessed　based　on　the　in-situ　test　findings　from　the　clay　foundation.