Variability Of Soil Nonlinear Dynamic Feature And Probability Analysis Of Its Effect On Ground Motion

The relationships of dynamic shear modulus and damping ratio with shear strains,i.e.G/G_max-γandλ-γcurves,of soil are two vital parameters in soil dynamic nonlinear analysis.It is indispensable to seismic safety evaluation of engineering sites and seismic microzonation as well. Because of the variability of soil itself and different testing techniques, the two parameters are of noticeable variability.Considerable work has shown that such variability of dynamic shear modulus and damping ratio dramatically influences earthquake ground motion.The anti-seismic design based on Probability and Reliability has already become a hot trend.However,the variability of soil and its effect on earthquake ground motion have not been solved with regard to the sense of probability at present.Consequently,it obviously falls behind the developing level of the anti-seismic study on the whole.Therefore,it cannot meet the demands of current engineering design.Based on the data of 588 soil samples from 42 cities of 17 provinces, the thesis presents the variability distributions of dynamic nonlinear feature of five soils,i.e.Clay,Silty clay,Silt,Sand,Mucky soil,and variable statistic indices.The change range of the dynamic shear modulus and damping ratio at different probability levels and typical shear strains are given.The results of probability analysis of the influence of dynamic shear modulus and damping ratio on response spectra are discussed as well as the rules of the influence.Thus it can improve the response spectra theories towards Reliability so as to support anti-seismic design based on Probability and Reliability.The main work in this thesis includes:1.The present research on soil dynamic modulus and damping ratio, uncertainty of soil parameters,impact of soil dynamic modulus and damping ratio on earthquake ground motion are summarized and testing techniques of soil dynamic feature are also introduced.2.The calculating method of reference range and testing method of data distribution is discussed in detail and the responding calculating program is formed.3.Variability distributions of five soils at eight typical shear strains are studied and the variability statistic indices are given.4.The change range of dynamic shear modulus and damping ratio at different probability levels and typical shear strains are given and the change rules are analyzed. 5.For typical sitesⅡandⅢ,the rules of the influence of dynamic shear modulus and damping ratio at different probability levels on ground accelerations under artificial earthquake ground motions with different peak values and spectra properties are discussed.The probability analysis results of dynamic shear modulus and damping ratio to response spectra are also given.