Study On Seimic Ground Motion On Liquefiable Soil Layer And Site Liquefaction Detection

Sand liquefaction is an important problem by many scientists focusing in the world. In China, the hazard liquefaction-induced is serious in the past and the structures are threatened by earthquake liquefaction in the future. So it is always a forward subject in earthquake engineering.In this paper, three problems are investigated. The first one and the second one is the effect of liquefaction on acceleration and displacement, separately, which is from the view of the soil layer is the media of the vibration and the source of the displacement of the structure. They are forward problems. The third one is the detection method of liquefaction by earthquake records, which is the inverse problem of ground motion.In this paper, the relation studies have been summarized and anglicized and the defects have been found. On this base, the key points have been studied by earthquake investigation, experiment and numerical analysis. The main works are:1. By dynamic triaxial test, the model of pore water pressure under complex consolidation is studied. A new formula which is can be used for calculating the water pressure of saturated sands under anisotropic consolidation is presented and the simplified method of evaluating the pore water pressure time history is established. Their reliability are all tested and verified.2. The limitation of the ground motion analyzing method using for liquefied soil layer is pointed and a effective stress method is presented. This method is tested by real earthquake records and shaking table test.3. By analysis of the earthquake records, shaking table test and numerical analysis, the feature of the liquefied soil motion is found, including the influence of liquefied layer on design response spectrum and site classified and the knowledge of effect of liquefaction on the long period of response spectrum. The liquefaction increment response spectrum and the liquefaction modified response spectrum are presented.4. The liquefaction on the ground dynamic displacement is investigated through earthquake records, shaking table test and numerical analysis. The characteristic of liquefied ground displacement is found and the liquefaction increment displacement response spectrum and liquefaction modified displacement response spectrum are present.5. For the theory shortage of detecting liquefaction from earthquake records, the physical nature is analyzed and a new method of the frequency decrease rate for fast identification of site liquefaction from surface acceleration records is presented. The liquefiable site is simplified as a double-degree-freedom model l and the formula for calculating the reduction of horizontal natural frequency induced by liquefaction is attained. And then the lower limit of frequency decrease rate is derived and based on it, the fast identification method of site liquefaction from surface acceleration records is proposed. The reliability of the method is examined by actual earthquake records...