Bouc-Wen Dynamic Model For Soils And Its Threshold Strain

The relation between stress and strain under dynamic loading for soil is the basic content in soil dynamics and the foundation in analyzing the dynamic response of soil, etc. The main characteristics showed are nonlinearity, hysteretic nature, the accumulated deformation, etc. So far, the dynamic models for soil are still not good enough while the Bouc-Wen model contains nonlinear damping and stiffness, good at describing the aforementioned dynamic response of soil under dynamic loading with various kinds of hysteresis loops by fitting the parameters properly. The Bouc-Wen model is good at programming and universal without dealing with the turnoff point in loading for different types of soils.Based on the introduction of the classical Bouc-Wen model, the modified deteriorated Bouc-Wen model is proposed. The physical meaning and influence of parameters on hysteresis loops, certain conditions applying to soil constitutive model are analyzed.The paper adopts the genetic algorithm to get the laws of parameters according to the fitting of dynamic shear modulus and damping resulted from dynamic tests. Then the research discusses the parameter identification of the real hysteresis loops directly resulted from dynamic tests by use of the least square method after the linearization of expressions.Finally, using the thermodynamic methods, this paper constructs dynamic dissipation function considering the shear modulus and damping resulted from dynamic tests together while the Hardin-Drnevich model and the Ramberg-Osgood model do not consider this. Then the energy dissipation characteristics and dynamic deformation mechanism of damming earth and rocks are analyzed and two threshold strains are found defined as the first threshold strain and the second threshold strain respectively. The second threshold strain is equated with the traditional threshold strain using pore water pressure build-up or volume changes as standard.