Experimental Study On Nonlinear Three-dimensional Rheological Constitutive Model Of Q₃ Remolded-loess And Its Implementation In FLAC3D

With the rapid development of the western loess region and engineering construction, the practical problems of the loess deformation, strength and stability in the engineering construction are increasing, which is related to the time. For example, the stress on anti-slide piles and retaining walls changes over time, the slope becomes instable and fails over time, the foundation settlement increases. When research the mechanical properties of loess and the problems of deformation and strength of loess, considering rheological properties of loess has significance to guide the engineering construction. At the same time, the development of the computer makes the application of the numerical calculation method in the research of the loess stability problems more and more widely, become an important method in the research field, however, because of the complexity and diversity of soil, constitutive models in the numerical software cannot satisfy the need of practical engineering. Based on this, this article set Q₃ remolding loess as the research object, carried out the following work:Through the triaxial cyclic loading and unloading creep test, obtained creep curves and the failure pattern of Q₃ remolding loess under different confining pressure, and drawn the corresponding relationship between strain rate and time under confining pressure curve and the curve of stress-strain relationship in the same time. Triaxial loops and unloading rheological test showed that under low stress and high stress condition, creep strain rate decreases with the increase of time, characterized by primary creep; Only in the condition of high stress, creep strain rate through first decreases, and smooth, increase the final three process, corresponding to primary creep, steady creep and accelerated creep three stages. Specimens produced certain instantaneous elastic deformation under different stress. Under the same confining pressure, the accelerating period of time reduced along with the increase of stress at the time of sample damage. The stress of specimen damage increased with the increase of confining pressure. Sample once appeared steady creep will lead to accelerated creep to make sample damage. Loess rheological with nonlinear characteristics, the stress strain curve skew to the strain axis gradually as the increase of stress level, the nonlinear degree enhanced along with the increase of stress.Base on uniform rheological mechanical model theory, obtained the three-dimensional rheological constitutive model of Q₃ remolding loess, deduced three-dimensional constitutive equation and identifies the model parameters, drawn the model primary creep curve and test curve contrast figure, shows the model reduction creep curve anastomose with the test curve, the model parameters is good, the model can well reflect properties of Q₃ loess in the primary creep stage. In order to describe the accelerating creep stage, put forward nonlinear rheological model, obtained three-dimensional rheological constitutive and the model parameters, drawn the model creep curve and test curve contrast figure, shows the model creep curve anastomose with the test curve, the model parameters is good, the model can well reflect properties of Q₃ loess.According to the relation of deformation rate and time curve, get long time strength value of Q₃ reshaping loess. Using score-linear equation method, established the three long-term strength equation under corresponding confining pressure, and determined the long-term strength values. Compared the two methods, the long-term strength concluded by two methods increased as the increase of confining pressure. Under the same confining pressure, the long-term strength obtained by the deformation rate relationship curve is less than the value of the long-term strength obtained by score-linear equation, is more conservative when applied in practical engineering; there is the difference between the value of long-term strength get by two ways, but the difference is not big, the difference is mainly due to when get the value of the long-term strength according to the deformation rate and time curve, the relationship curve of stress interval will affect the determination of inflection point.Base on nonlinear rheological model of Q₃ remolding loess, deduced central difference form of three-dimensional constitutive equation, used the secondary development program interface provided by FLAC3D（version 4.0）, compiled FLAC3 D dynamic link library program of Q₃ remolding loess nonlinear rheological model. Used the numerical procedure, though simulating triaxial rheological test under different confining pressure, verified the FLAC3 D numerical procedure of nonlinear rheological model.