Nonlinear Probabilistic Dynamic Response Analysis Of Effective Stress Of Earth Dams Under Nonstationary Seismic Loadings

In this dissertation, the probabilistic seismic response of liquefiable foundations and earth dams was carried out via stochastic finite element method under nonstationary seismic loadings. The following work was finished mainly:1. The nonstationary power spectral density (PSD) of acceleration at the ground level was obtained by an iterative approach of equivalence of peak acceleration according to the response spectrum in the Chinese seismic code (GB 50011-2001). After the stiffness and damping ratio of each soil layer were evaluated by the equivalent linearization technique and by the use of the one-dimensional wave propagation function on the semi-finite shear beam, the earthquake motion at bedrock under nonlinear layered ground was evaluated iteratively. In this frame, the nonstationary seismic model according to the seismic code was presented It provides relatively reliable and accurate earthquake motion input at the bedrock for the stochastic seismic analysis.2. Based on the Biot dynamic consolidation equation of the saturated porous medium, a set of u-p form two-dimentional finite element methods was established. Hardin-Drnevich constitutive model was applied accounting for the nonlinearity of soil. The effect of pore pressure and residual strain on dynamic response was considered as initial strain base on the data of cyclic triaxial tests and seismic settlement tests. The right members of the Biot dynamic equation was divided into two parts. The first part was zero mean value vibration corresponding to earthquake acceleration corresponding and the second part was the mean value corresponding to initial strain. The pseudo excitation algorithm was introduced to the first part accounting for the stochastic nature of earthquake. The equivalent shear modulus, damping, excess pore water pressure and residual strain induced by seismic loading were estimated by the interpolation method based on probabilistic average approach. In this frame, the nonstationary dynamic probabilistic response of soil was obtained in frequency domain and time domain under stochastic seismic loadings. The results were presented as evolution self-PSD and cross- PSD of dynamic response.3. By a half-quantitative and half-qualitative method, the exactness of the dynamic finite element was verified. The boundary condition and boundary range were determined by the compared result of dynamic response of different range of foundation. The results show that the truncated boundary can meet the precision demand of the dynamic calculation when the boundary is 5 time as the range of the foundation to study.4. The stochastic dynamic response of level ground was carried out by total stress method, undrained effective stress method and drained effective method. Also, the performance of four techniques, using different approximation to estimate the equivalent peak value of shear stress and strain were investigated for the purpose to determine the equivalent shear modulus, damping, excess pore water pressure and residual strain induced by seismic loading, in which the equivalent peak value was computed in terms of its standard deviation and the corresponding peak factor. It is found that the interpolation method based on probabilistic average approach is appropriate compared to the mean value of deterministic method.5. The stochastic dynamic response of a typical section of embankment was analyzed in the project of Qiantang River anti-flood embankment. The results indicate that the analysis method put forward in this dissertation is of great practical importance in seismic design.