Study On Dynamic Characteristic And Damage Law Of Loess In Xianyang

Loess is a kind of special soil which is widely distributed in China, and it mainly distributes in the northwest loess plateau area. This area is the seismic belt and of high intensity. In the history, the geological problems which were caused by earthquake such as landslide and collapse, settlement deformation and liquefaction, ground fissures, ground base and foundation subsidence deformation, and many other disasters caused much loss to the local. With the development of the economy and society of western China, all kinds of large engineering become more and more. The research of the dynamic characteristics of loess is also getting more and more important for engineering. The research has wide coverage. The domestic and foreign experts havedone many researches of the dynamic characteristics of loess. Generally the moisture content, density, loading frequency and processing method of the test results of these researches are different. And researches which are about the dynamic characteristics and strength damage law of loess under different types of load are less.In this paper, on the basis of the National Natural Science Fund Project "the research of microstructure and strength evolution of typical loess under different types of dynamic load", basic physical and mechanical properties of the sample are tested. Then sine wave and square wave load rating dynamic triaxial tests are done. The impacts of confining pressure, consolidation ratio and type of load on dynamic characteristics are analyzed. Then the evolution of shear stress distribution and plastic zone in dynamic load process is simulated by FLAC3 D. Compared with experimental results, the deformation mechanism of loess in Xianyang under dynamic load is analyzed. At last, the law of dynamic elastic modulus with cumulative damage variable under sine square wave load and square wave load is analyzed through variable linear cumulative damage theory, and its causes are discussed.In the study of this paper, it can be found that the constitutive curve of loess in Xianyang has obvious nonlinear characteristic under conditions of sinusoidal load and square wave load, and this curve can be described by Hardin-Drnevich hyperbolic model. Consolidation ratio, confining pressure and the type of dynamic load, all of them have corresponding effects on the dynamic properties of loess in Xianyang. Results of numerical simulation show that the relatively tensile stress area and the shear stress area are mainly in the lower part of the model, this can explain the phenomenon that the more serious damage produced in the lower part of sample in test. With the increase of vibration times, it can be found that the cumulative effect of shear stress and tensile stress in the lower part of the sample causes the loss of dynamic strength and leads to the occurrence of breaking in stress cloud figures and plastic zone distribution maps. Compared with the sine wave load, the effect of shear stress and relative tensile stress is more obvious under square wave load in the lower part of the model, and the model is more susceptible to be damaged. In the dynamic case, dynamic elastic modulus of loess in Xianyang is decreasing with the cumulative damage and eventually tends to a constant value. The relationship between the amount of damage accumulation and the elastic modulus is approximated power function. Compare to square wave load, dynamic elastic modulus under sinusoidal load can tend to value under small degree of damage. At the same cumulative damage variable, the corresponding dynamic elastic modulus increase with the increasing of consolidation pressure. For the samples of same consolidation stress state, the dynamic elastic modulus under the sine wave load is greater than the dynamic elastic modulus under square wave load.