A creep model for frozen sand of Qinghai-Tibet based on Nishihara model

摘要

The tri-axial creep tests of frozen sand with different dry densities and grain size distributions were performed at 0.1 MPa confining pressure at different temperatures. The results show that the rheological properties of frozen sand are significantly affected by the temperature, the creep deformation of the frozen sand is obvious even under a small load when the temperature is higher than - 1.5 degrees C. Firstly, based on the Nishihara model, the elastic modulus of viscoelastic elements is modified to be a function of stress, the coefficient of viscosity in viscoelastic part is modified considering the effect of time and stress, and the viscoplastic element is improved by introducing the damage variable. Then a new non-linear creep constitutive model for frozen sand is proposed, and the new model is verified based on test results. It can be found that the predicted results agree well with the corresponding experimental results from low stress to high stress, and the proposed model can describe the whole creep process of frozen sand with different dry densities and grain size distributions accurately under different shear stress levels and temperatures. Besides, the function relationship between the model parameters and the shear stress under different temperatures is obtained through the regression analysis. Finally, the influences of the temperature and shear stress on the parameters are analyzed as well. This study is important to further study the stability of permafrost subgrade, and can accumulate experimental data for the study of creep theory.