Experiment And Application Studies On Dynamic Shear Modulus And Damping Of Geotechnical Media

The dynamic shear modulus and damping ratio of soils are two important parameters in the soil dynamics and they affect earthquake ground motion in a great extent. First, the existing situation of research on modulus and damping ratio is reviewed and the shortages in the research work are pointed out. Then, the dynamic modulus and damping of soils are studied from three angles including the experimental technique, experimental study and application. Using tests, theoretical analysis and numerical simulation, several typical problems such as the experimental technique and reliability, experimental theory and their application in engineering are discussed in this paper. The main works and achievements are:1. Two important problems about the resonant column device in the experimental technique and analytical method of reliabilityFirst, the reliability theory of routine tests for the fixed-free resonant column device is developed and the analytical method and technique of reliability are presented. The error equations of modulus, strain and damping ratio are obtained by the root mean square method. The affecting factors and affecting degree of error are analyzed. Then the reliability of routine tests for a new device is successfully investigated according to the method and technique.Second, a revised coefficient method is presented in order to obtain the dynamic shear modulus of the rigid samples. The analytical method and technique of the reliability for the multipurpose resonant column device is established, including analyses for the test error, frequency error of tests, correlation of test results and the accurate of the revised curves. The error equations of modulus, strain and damping ratio are obtained by the root mean square method. The affecting factors and affecting degree of error are analyzed. Then the reliability of the rigid samples tests for the new device is successfully investigated according to the method and technique. The results here indicate that the revised coefficient method and curves presented in the paper are reliable and the new device is accurate and stable as well. As a result, the device can be used for testing the dynamic shear modulus of the rigid materials in small strain range.2. The effects of the anisotropic consolidation on the maximum dynamic shear modulusA new formula for evaluating the maximum dynamic shear modulus of the sand under the anisotropic consolidation is presented by using the multipurpose resonant column tests and dynamic triaxial tests. The suitable form of the new formula is to use the power function to describe the relation between the relative increment of the maximum dynamic shear modulus due to the anisotropic consolidation and the increment of the consolidation ratio, AGm/G0m =C.(kc -1)~B. The new formula indicates that the maximum dynamic shear modulus is the power of the kc-\ and quite differs from nearly straight relation of Gm/G0m-kc in Hardin's formula. It also indicates that the increasing degree of the maximumdynamic shear modulus due to kc >1.0 is significantly larger than that describedby Hardin's formula.The effects of the anisotropic consolidation on the non-linear behavior of the dynamic shear modulus are obtained and the results show that anisotropic consolidation makes the normalized dynamic shear modulus of the sand larger in a certain degree.3. Three problems in the application of the dynamic shear modulus and dampingFirst, the reasonability of the dynamic shear modulus and damping ratio in the aseismic code and recommended by Yuan et al. is studied by comparing the existing testing results and analyzing their effects on earthquake ground motion. Compared with the results in the code, Yuan's results are more reasonable. The latter is much agreeable with the existing results and the unreasonable phenomena in earthquake ground motions can be avoided. The recommended values can be used in the practice and in revising the code.Second, the effects of dynamic modulus of soil under different consolidation ratios on earthquake gro...