Abstract：By using the technology of Hankel transform，the torsional vibration of a rigid circular plate resting on double-layered subgrade overlaying bedrock is discussed. Taking the soil above the groundwater table as elastic single-phase layer and the soil below the groundwater table as saturated medium，considering the mixed boundary condition at the upper surface，the fixed boundary condition at the lowest surface and that the stress and displacement at the interface of the layers are continuous，the dual integral equations are established. By mathematical methods，the dual integral equations are reduced to Fredholm integral equations of the second kind. Subsequently，the dynamic compliance coefficients of the foundation，the equivalent stiffness and equivalent damping of the subgrade，the angular amplitude of the foundation are expressed explicitly. Selected numerical studies indicate that the height of the stratum and the shear moduli¢ ratio between the layers have pronounced effect on the results.
