Research On Deformation Behavior And Constitutive Model Of Sands Under Cyclic Rotation Of Principal Stress Axes

The study on the stress-strain characteristics and constitutive model for soils subjected to cyclic rotation of principal stress axes is one of the hot topics and most difficult problems in the research field of soil dynamics, which has been paid much attention by many researchers in the worldwide but still unresolved well. Presented in this dissertation are experimental facts, physical interpretation, theoretical formulations and numerical analysis which were made systematically for the purpose of investigating the deformation behavior of sands under cyclic rotation of principal stress axes. The main achievements could be summarized as follows.1. The basic stress-strain characteristics and related physical mechanisms for sands under cyclic rotation of principal stress axes were investigated based on three kinds of drained tests including fixed principal stress axes, cyclic rotation of principal stress axes with magnitudes of principal stresses kept constant, and cyclic changes of principal stresses in both their axes and magnitudes. The main deformation behavior of sands with inherent anisotropy under cyclic rotation of principal stress axes with magnitudes of principal stresses kept constant was obtained in the following. 1) The plastic deformation induced due to cyclic rotation of principal stress axes alone can be in the same magnitude as that due to shear with fixed principal stress axes. 2) The volumetric strain due to shearing of cyclic rotation of principal stress axes is found to be composed of a reversible dilatancy component and an irreversible dilatancy component. The former is characterized by its reversibility and is independent of past shear history, the latter by its irreversibility increases with the increase of cycle number yet its increase rate decreases with its accumulation. 3) The obvious non-coaxiality between directions of the principal stresses and principal strain increments is found and its degree depends largely on the change of shear stress component. 4) The intermediate principal stress has considerable effects on the deformation behavior of sands in the condition of cyclic rotation of principal stress axes. The accumulation rate of the irreversible dilatancy component increases with the increase of the intermediate principal stress parameter. Under the condition of combined variation of principal stresses axes and magnitudes, the initial deviatoric stress and its variation range have considerable effects on the deformation behavior of anisotropic sands.2. A new cyclic constitutive model for sands which can describe the deformation behavior of sands under combined variation of principal stress axes and magnitudes was developed based on the above physical fundamentals. And its effectiveness under the complex stress paths including cyclic rotation of principal stress axes is verified by a good comparison of model simulation with test results for sands. The obvious advantage of the constitutive model is confirmed by the reasonable prediction of the developments of strain components and volumetric strain in various conditions including principal stress axes rotation.3. A pragmatic stress integration algorithm of the model was developed and incorporated into the FEM software of MSC.Marc. The responses of a typical dam under the wave loading indicated that the deformation of the dam increases if the effects of principal stress axes were considered.