R-O Model With Varying Parameters For Dam Materials And Its Thermodynamic Explanation

The dynamic characteristics of dam materials are important parameters for dynamic analysis of dam, it is directly related to results of dam's seismic. response and affect the seismic design. In engineering practice, a direct dynamic test was taken to determine the dynamic parameters in the large scale dam project, but in the other hand, analogy method was used in the middle-small scale dam project. It is many influence factors in dynamic test of dam materials and test results have certain discrete. Even though the test of the large-scale dam project is conducted, due to the change of dry density of dam design material and the complexity of site construction conditions, even the characteristics of large-scale cyclic triaxial tests are long period, high cost and limited number of test group, thus parameters from laboratory test are also difficult to reflect the actual fully. Therefore, the larger-middle scale dam project usually needs sensitivity analysis of dynamic parameters. Soil dynamic parameters include two parts, one is the maximum dynamic shear modulus parameter and the other is the variation of the modulus ratio and damping ratio with the variation of dynamic shear strain. On the basis of existing test data which were systematically analyzed again and summarize both at home and abroad, then establish unified mathematical expressions for their relative curves, which are nonlinear variation about dynamic equivalent shear modulus and dynamic damping ratio with shear strain on dam materials,including rockfill materials, core materials and anti-filter materials. In addition, discussed the normalized dynamic damping ratio relating to the normalized dynamic equivalent shear modulus, and provided modification of recommended formulas. These formulas can be used to determine the reasonableness of the dynamic test results and also can be directly used as dynamic parameters of the sensitivity analysis of the dam and the dynamic parameters of the middle-small scale dam project.Based on 2D-FEM analytical model of 200m high core dam, the dynamic results of the dam materials in the different dynamic properties is discussed. In process of calculation, taking different combinations of average curve and double standard variances of up-down curves about the dynamic damping ratio and the dynamic equivalent shear modulus of rockfill materials, core materials and anti-filter materials as working conditions of dam materials, analyze the sensitivity of the dynamic properties of dam. The results show that the dynamic characteristics of dam materials are the key factors to describe all dynamically analyzed during a seismic design of embankment dam. For establishing dynamic constitutive model of the modulus and damping mean curve about rockfill materials, core materials and anti-filter materials, take the dynamic parameters of Xinlian material in different confining pressures as an example. Described three solution methods for reference shear strain of different values, and discussed their application characteristics of the three methods. To compare the result of calculating the reference shear strain of the three methods, make the goodness of fit as an indicator to measure the level of the respective normalized of the reference shear strain on the dynamic parameters after the normalization. Finally, Calculate reference shear strain of three kinds of the mean curve about dam materials, rockfill materials, core materials and anti-filter materials, by the highest degree of normalization calculation method. And establish dynamic constitutive equation, adapting their mean curves, which is the Ramberg-Osgood constitutive model with variable parameters.By taking the Ramberg-Osgood constitutive model with variable parameters as the research object, establish expression of parameters R (y) and (y) with the independent variable shear strain, relating to the mean curve equation of three dam materials, and discuss their applicable conditions. Then base on the Ramberg-Osgood constitutive model with variable parameters, start from the basic laws of thermodynamics, constructed the free energy function and the dissipation function of three materials when the plastic movement of the center of a straight line. Research their dynamic dissipation characteristics and mechanisms of dynamic deformation, draw the dissipative stress space and the real stress space of the yield curve and reached their threshold strain.The calculation method is improved On the basis of the past, compared with the usual, with a more adaptive, and can be applied to different dam material.