Research On Cyclic Elasto-plastic Constitutive Model For Rockfill Materials And Its Application

Permanent deformation of rockfill materials is the main cause of seismic damage of rockfill dams. Prediction of earthquake-induced permanent deformation is therefore quite important in design of rockfill dams. The viso-elasto-plastic model widely used in current seismic response analysis can only provide an empirical and rough prediction of residual deformation. Using cyclic elasto-plastic model can avoid this shortage. This paper presents a practical three-dimensional(3D) cyclic elasto-plastic model of rockfill materials, which is based on previous experimental facts and findings of the stress-strain characteristics of rockfill materials. Corresponding numerical procedures are developed based on the open source finite element program OpenSees. The main achievements presented in this paper are summarized from the following three aspects:Firstly, a 3D cyclic elasto-plastic model for rockfill material is developed, which can reasonably capture the main features of the stress-strain behavior of rockfill material. The model has several distinct advantages in comparison of other existing cyclic elasto-plastic models: 1) A double parameter 3D nonlinear strength criterion is proposed based on modification of the spatial mobilized plane(SMP) criterion, which simplifies the description of shear strength of rockfill material under cyclic loading. 2) The model can reflect accumulation of irreversible volumetric strain under cyclic deviatorc stress or cyclic spheric stress, and their coupled effects. The description of volumetric strain under any cyclic loads is more reasonable and accurate. 3) The model can describe hysteresis, hardening and accumulation of the shear strain under cyclic shear stress, which can more finely calculate the shear strain of rockfill material during cyclic loading. 4) The model has only 11 parameters in total. All of them can be calibrated by conventional dynamic triaxial test results including maximum shear modulus, degeneration curve of shear modulus as well as cumulative curve of residual strain with increasing number of cycles, which make the model more practical.Secondly, numerical methods using the new constitutive model are proposed. Practical codes are incorporated into the OpenSees program, and corresponding pre- and post-processing programs are developed to actualize efficient modeling of rockfill dams. Analyses of idealized 2D dam and homogeneous 3D dam are performed. Essential effectiveness of the methods and programs are confirmed.Finally, a 3D dynamic finite element analysis is performed to simulate the response and deformation of the Zipingpu CFRD subjected to the Wenchuan earthquake. The simulated residual deformation basically coincides with the measured data, showing the feasibility of the presented model and corresponding numerical methods.