Study And Application On Soil's Constitutive Model With The Consideration Of Stress-induced Anisotropy

Stress-induced anisotropy is one of very important characters of soil and also key difference from metal material, which exist in many geotechnical projects. It is very important to stimulate and reflect the anisotropy in the process of study on soil's constitutive relationship. To establish a reasonable anisotropic constitutive model will supply some new methods to solve some practical problem. Study on the stress-induced anisotropy is very important in terms of theoretical analysis and practical engineering.Based on series true-triaxial tests under complex stress state, basic anisotropic deformation mechanism and mechanical characteristics of soil is discovered, which will supply enough data for the establishment of anisotropy constitutive model. Based on the test results, the main character of the strain-stress matrix of soil under complex stress state is summarized. It is summarized that the shape and form of the strain stress matrix of soil elements under complex stress state, which may be used to verify and check the correct and rationality of soil's constitutive model.By considering the stress-induced anisotropy under complex stress state, based on the usual-used Duncan-Chang model, a new anisotropic model is developed, which can describe the stress-induced anisotropy and is convenient by applying the same parameter as Duncan-Chang model.To apply the new model in the FEM, the coordinate transformation method is discussed. The anisotropic finite element format of planar is derived. By making some necessary changes to the BCF FEM codes, an anisotropic 2D FEM program is given, which apply the new anisotropic model. A simple example is analyzed and it is shown that the anisotropic model is superior to conventional non-linear elastic model on aspect of reflecting the anisotropy and the program is reliable.Compared with conventional Duncan-Chang E-v and E-B model, the anisotropic model was applied to perform the 2D Fern analyses on the practical rockfill dam. The results showed that conventional model couldn't stimulate the stress-induced anisotropy produced during the process of reservoir impoundment, which will bring major error of stress and displacement calculation in the concrete faceplate and also will influence the hydro fracture in the earth core rockfill dam. Anisotropy model can stimulate this character to some extent. A new elastic-plastic model is also presented based on the Cam-clay model with the consideration of initially stress anisotropy. This model was developed by modifying the Sekiguchi-Ohta model using a new stress parameter and adjusting the yield locus and hardening axis in the p-q plane, which will improve the calculated results. A simpleexample is analyzed by FEM with the new model. The result is compared with that got from Cam-clay model and Sekiguchi-Ohta model; it is shown that new anisotropic model is superior to original model.