Correlation Theories And Interaction Rules Of Subsoil Degradation And Ground Motions

Macro earthquake-investigation experiences demonstrate that the effects of soft sites, subsoil nonlinearity and liquefiable layers on the damage to superstructures, foundations and underground structures are tremendous. The effects of seismic loading on engineering structures mainly take the forms of inertia forces and soil deformation. To superstructures, the influence of inertia forces is predominant. The design response spectra have incorporated subsoil nonlinearity and are controlled by ground acceleration response spectra. To foundations and underground structures, however, subsoil-deformation act which is controlled by ground displacement response surpasses inertia forces.Subsoil degradation principally represents in three aspects, i.e., (1) natural soft sites; (2) soil nonlinearity induced by subsoil degradation under strong earthquakes; (3) subsoil degradation caused by liquefaction. The three aspects specially influence acceleration response spectra and soil deformation. Actually, seismic waves result in subsoil degradation; meanwhile, subsoil degradation conversely alters seismic waves. It is a typical seismic waves-subsoil degradation interaction problem. The crucial point for the interaction is to comprehend the correlation and interaction rules of seismic waves and subsoil degradation. Nevertheless, currently the mechanism and interaction rules have hardly been wholly acquainted. A quantitative relationship between soil degradation and ground motions has not yet been manifested and theoretical explanations are quite limited.In the thesis, subsoil degradation including liquefaction and ground motions are simultaneously considered. Taking correlation theories and interaction rules as a theme, simplified theoretical models and relevant solutions both in frequency domain and in time domain are proposed employing wave propagation theories and dynamic principles. The influencing parameters are analyzed individually. Preliminary quantitative correlations and interaction rules of subsoil degradation and ground motions are illustrated. The main salient points and achievements obtained can be outlined:1. By means of large shaking table tests, the influence of soil liquefaction on ground motions has been investigated along with ground motions characteristics with increasing excess pore-water pressure. Ground motions and deformation progress resulted from subsoil degradation and deterioration under dynamic loadings are described and characteristics of ground motions are presented.2. Analyzing the existing pore-water pressure buildup models, a modified pore-water pressure incremental model for horizontal strata and the relevant procedure to calculate pore-water pressure process are proposed. Using the Cycle-by-Cycle method, pore-water pressure buildup process under irregular seismic loadings can be calculated. Eventually, the modified model is testified by the large shaking table testing results.3. Simplified models, which consider subsoil degradation, are established for simulating horizontal engineering sites. By steady-state wave solutions in frequency domain the theoretical solutions for ground motions, i.e., displacement and acceleration, under harmonic waves are deduced. Through parameter analysis, the influencing factors and the influencing rules of subsoil degradation on ground motion response are discussed. The progress of subsoil degradation and postliquefaction characteristics have been elucidated.4. Exploring the proposed simplified models and Fourier and Reverse Fourier Transform methods, a theoretical solution in time domain for ground motions under dynamic loadings is presented. By numerical calculation, the characteristics and influencing rules of subsoil degradation on ground motions are analyzed. The reasonability and reliability of the solution are verified by large shaking table testing results.5. Analyzing the theoretical solutions in time domain and in frequency domain of the proposed simplified models, quantitative characteristics of subsoil degradation and seismic wave spectra are extracted. Quantitative influencing indices are defined and proposed. The correlation and interaction rules of subsoil degradation progress and seismic wave characteristics are established. Preliminary acquaintance of the correlation and interaction rules are obtained.