Study On Fractional Rheological Constitutive Model Of Q₃ Loess

In the process of advancing the development of the western region and the sustained and healthy development of the economy and society in the western region,infrastructure construction remains the main weak link in the development of the western region.Especially the development of loess in northwestern China,due to the obvious time effect of the deformation and destruction of loess,under the long-term load,such as tunnel surrounding rock,slope,retaining wall,foundation and roadbed may creep rheological phenomena,such as progressive damage,have an adverse effect on the smooth implementation of the project construction and the later safety operation and maintenance.Therefore,it is of great theoretical and practical significance to analyze the rheological mechanism of loess and study its creep characteristics and constitutive models.The thesis takes Q₃ undisturbed and remolded loess as the research object.First,based on triaxial cyclic loading and unloading rheological tests,the complete creep curves of Q₃undisturbed and remolded loess under different confining pressures are obtained.On this basis,based on the unified rheological mechanics model theory,considering the characteristics of the loading and unloading creep curves under different load levels,the creep constitutive model of Q₃ undisturbed and remolded loess was identified,and the elastic body,elastic an improved Nishihara model composed of four parts of plastic body,viscoplastic body and viscoelastic plastic body connected in series.Secondly,based on the fractional derivative theory,a new fractional nonlinear loess creep constitutive model is proposed,and its one-dimensional constitutive equation is derived.Based on the Q₃ undisturbed and remodeled loess creep test data,the model was fitted and the model parameters were obtained by solving.The comparison and analysis with the integer order creep model and the test curve verify its accuracy and superiority.Finally,the one-dimensional constitutive model equations are generalized to three-dimensional,and the three-dimensional central difference form of the model is derived,and the secondary development of the model in FLAC3D is realized through the VISUAL STUDIO development environment.The dynamic link library program of the model is compiled.The simulation of the loess triaxial rheological test verifies the correctness and rationality of the numerical program of the model,which lays the foundation for the numerical application of the model and practical engineering applications.Studies have shown that the fractional creep constitutive model is in good agreement with the test curve as a whole,especially in the deceleration creep and unloading phases.Compared with the integer-order model,the fitting effect is better and the fitting accuracy is higher.At the same time,the fractional order model makes up for the shortcoming that the integer order linear model cannot describe the acceleration creep stage.