Long-term　cyclic　loading　applied　to　clay　at　stress　levels　lower　than　the　critical　cyclic　stress　leads　to　soil　deformation　without　inducing　damage.　The　Monismith　model　is　well-known　for　its　simplicity　and　ability　to　describe　the　trend　of　cumulative　plastic　strain　under　cyclic　loading.　However,　the　simulated　cumulative　plastic　strain　increases　indefinitely　with　the　number　of　cycles　until　damage　occurs.　At　lower　cyclic　stress　levels,　the　cumulative　plastic　strain　tends　to　be　stabilized　with　an　increasing　number　of　cycles,　ultimately　limits　the　applicability　of　the　model.　To　address　this　issue,　a　series　of　axial-torsional　bi-directional　cyclic　loading　tests　are　conducted　on　saturated　clay　using　a　hollow　cylinder　torsional　shear　apparatus.　An　empirical　three-parameter　mathematical　prediction　model　is　proposed　by　analyzing　the　development　of　cumulative　generalized　shear　strain　based　on　test　results.　The　relationships　of　model　parameters　a　with　plasticity　index,　frequency,　generalized　shear　stress,　and　mean　effective　stress;　b　with　plasticity　index,　and　c　with　frequency　and　plasticity　index　are　presented　as　functional　expressions.　Finally,　the　predicted　results　of　the　empirical　model　are　compared　with　test　results　to　verify　its　effectiveness,　providing　a　basis　for　calculating　cumulative　deformation　in　clay　under　long-term　low　cyclic　stress　levels.