Study On The Relationship Of Soil Permanent Deformation And The Characteristics Of Seismic Loading

In terms of recent catastrophic earthquakes, the earthquake-induced settlement and large deformation of soft subsoils contribute significant effect on the engineering structural damage. The traditional seismic design of structures and foundations has gradually transferred from strength-based philosophies to deformation-controlled philosophies. The analysis of soil deformation has become more and more important.The fundamental task of soil dynamics and geotechnical earthquake engineering is to constitute the relationship between earthquake loading and dynamic stresses in the soil, i.e. the constitution of the relationship between the soil deformation and the parameters of ground motions. However, the current research work seldom considers two aspects, i.e. (1) the acquaintance of the asymmetry and irregularity of seismic waves; (2) the influence of the asymmetry and irregularity of seismic waves on the soil dynamic properties and the corresponding effective analytical methods.In this thesis, the author systematically summarizes and analyzes the previous research and obtained achievement in China and other countries on the subjects and shows the existing limitations and the direction for future research. Based on the laboratory results and the analyses of actual seismic recordings, moreover, some salient points on the conclusive and creative work can be outlined, including:1. In terms of dynamic interaction of saturated soil and structure, using small shaking table tests with sine wave inputting and large shaking table tests with actual seismic wave inputting, the relation of wave shape, dynamic stress under the bases of structure, dynamic pore water pressure, structure settlement and soil permanent deformation has been revealed and developed. The acquaintance of the relationship of soil deformation and ground motion properties comes more and more distinct.2. The concepts of cut-off ratio, peak value asymmetry ratio, amplitude asymmetry ratio and loading number asymmetry ratio are proposed. Through statistical analyses of the actual seismic recordings, the asymmetrical and statistical properties of amplitudes, peak values and loading times of seismic waves, loading types and wave series are presented.3. The concepts of strain threshold and effective loading have been proposed. According to the results of series of dynamic triaxial tests on clays and sands, the dynamic response of soil deformation to seismic loading is discussed herein. The relationship between the strain thresholds and the lower limits of effective loading for clay and sand is proposed. The formula and recommendation values for effective loading are given.4. Through series of dynamic triaxial tests, the soil deformation response under irregular seismic loadings and certain number of uniform-amplitude cyclic loadings has been discussed. A simplified method for evaluating the deformation of soil element under seismic loading and the influence of seismic loading parameters and soil properties on the modified coefficient are presented.