Abstract: This paper presents a multi mechanism model for the cyclic mobility of saturated sands in a 3D space. In the proposed constitutive model, the complex deformation mechanism is decomposed into a macroscopic volumetric mechanism and a number of 1D Equivalent Microscopic Shear Mechanisms (EMSM) in various orientations. Each 1D EMSM includes not only a shear deformation but also a volumetric deformation due to dilatancy, which are described by a microscopic stress strain relation and a microscopic stress dilatancy relation, respectively. The detailed relations between the macroscopic and microscopic material parameters are established. The accuracy of the model is confirmed by simulating the cyclic mobility of saturated sands for cyclic undrained torsional shear tests with and without an initial shear stress.