Elastoplastic Model for Sand and Clay Suitable For Describing the Cyclic Loading Response

Saturated sand has not only complex properties under static loading, but also complex deformation properties under cyclic loading. Under the cyclic loading of the drainage path, the plastic volume strain of sand will gradually increase with the number of cycles. The hysteretic loop formed by the varying generalized stress-strain relation changes structurally with the number of cycles, gradually from a relatively wide to a relatively narrow one. The tangent modulus represented by the hysteresis loop increases gradually. Under the cyclic loading without drainage, the cyclic mobility of saturated sand will appear. On the basis of the proposed unified hardening model, the original elliptic yield surface of fixed shape is changed to the elliptic yield surface with a variable rate of consolidation. The evolution relation of the short and long axes ratio is driven by plastic deformation, and the current stress ratio is employed to attribute the yield surface rotation axis. The law of rotational hardening is introduced to describe the anisotropy. The shape and position of the yield surface, and new hardening parameters coordinated with the behavior to the critical state are established. The 3D model considering complex loading conditions can be constructed by using the transformation stress method based on the SMP criterion. The validity and applicability of the proposed model are verified by predictive comparison.