Study On Liquefaction Characteristics And Liquefaction-influencing Factors Assessment

Post-earthquake investigation is the important way to gain seismic lessens and experience, meanwhile it is the base for aseismic theories and analytical methodologies. That is, engineering seismology cannot advance without earthquake investigations, typically vital destructive shocks. In the process of aseismic techniques evolvement in China, the deep post-earthquake investigations and in-situ field surveys and testing of previous earthquakes, e.g., Heyuan (1962), Xingtai (1966), Tonghai (1970), Haicheng (1975), Tangshan (1976) and Wenchuan (2008), have been greatly promoting engineering aseismic techniques and aseismic code formation in China.Earthquake liquefaction and relevant damage contributed considerable loss in seismic damage, and are kept close concern by geotechnical researchers and engineers. In the viewpoint of current achievements on liquefaction research, a big gap between the need for liquefaction mitigation and research exits typically in the fields of liquefied site characteristics and liquefaction-influencing factors based on real liquefaction field surveying materials and data, even though much progress has been realized. In recent years, the paucity of liquefaction research based on real liquefaction investigation data has restrained the advancement of geotechnical earthquake engineering and soil dynamics, which can be mainly summarized in the following. Macro liquefaction evaluation methods and investigation description standards in post-earthquake field survey cannot be found in literatures so that the overview of liquefaction scale and relevant loss in great earthquakes is hard to grasp. A systematic database of liquefaction documents and data is urgently needed for worldwide liquefaction documents and data archive. The field testing data analysis for site liquefaction in recent worldwide earthquakes has not been fully organized that the site characteristics revealed by real liquefaction data cannot be completely acquainted. The difference and coherence between Chinese liquefaction data and those of worldwide have not been identified, resulting in inappropriate understanding of the current status and future direction of liquefaction evaluation methods.Fairly abundant valuable liquefaction in-situ testing data from recent great earthquakes globally have been collected, which can be used to analyze the correlation of site characteristics and liquefaction. As a result, a novel acquaintance on the correlations of liquefaction responding to site property indexes, real dynamic loading intensity, soil conditions can be obtained so as to testify the current liquefaction evaluation methods.The main work and conclusions in this thesis can be drawn as fellow.1. Liquefaction data from48earthquakes globally have been collected to establish site liquefaction database. Soil layer conditions (i.e., sand buried depth, water tables), soil properties (i.e., relative density, particle diameter) and testing index (i.e., SPT) are analyzed so that the difference and common points in the site characteristics in China and other countries are comparatively portrayed. A complete and objective acquaintance of soil liquefaction is renewed to update the erratum and divergence in traditional liquefaction understanding.2. In terms of the need for post-earthquake investigation and current code updating, the concepts and corresponding classification of the macro-liquefaction index and macro-liquefaction grades are proposed in the thesis based on the thoughts and ideas conceived during liquefaction investigation in Wenchuan earthquake. The feasibility of the macro-liquefaction indexes and macro-liquefaction grades are testified by comparing the liquefaction data both in China and other countries. The macro-liquefaction indexes and grades can be adopted as the references for liquefaction investigation and evaluation, which provides necessary means for reliable liquefaction fundamental document collection and compilation.3. The liquefaction investigation materials and in-situ testing data in Wenchuan Ms8.0earthquake are systematically organized. Using the proposed macro-liquefaction indexes and grades, the liquefaction data and materials are analyzed to deep understand the liquefaction loss in the event. The macro-liquefaction indexes and macro-liquefaction grades in Chengdu, Deyang and Mianyang regions are depicted, while the seismic damage in liquefied and non-liquefied sites and the link of macro-liquefaction indexes with ground shaking are analyzed so that the liquefaction characteristics can be profoundly understood.4. In total,5103liquefaction data from51earthquakes worldwide are collected to explore the correlations of liquefaction with respect to PGA, ground water table, liquefied sand depth and site shear wave velocity by means of the Pearson product-moment correlation coefficient (PPCC) method. The correlations of liquefaction with the characteristic parameters under varying liquefied sand depth, ground water table and seismic intensity are comparatively analyzed. The correlations of liquefaction with respect to actual seismic loading and real sand buried conditions and in-situ site testing data are obtained and presented accordingly, including China mainland, Taiwan, Europe-USA and Japan. These can facilitate the understanding the relationships between liquefaction and soil layer parameters and ground shaking characteristics, and support to test the current liquefaction evaluation methods.5. The testifying of liquefaction discrimination formulae using SPT, CPT and Vs was performed by means of the liquefaction data-based correlation with respect to the site characteristics parameters using the collected liquefaction database. The reliability of the liquefaction discrimination formulae is evaluated that the erratum on the influence of soil layer buried depth on the CPT-based liquefaction discrimination formula is pinpointed. In the Vs-based liquefaction discrimination formula, the fact that the sand buried depth contributes too small in liquefaction evaluation is also revealed.6. Adopting the theories proposed in the thesis, the liquefaction data in Feb.22,2011, Christchurch New Zealand earthquake are selected to analyze the correlations of liquefaction with site characteristic indexes, i.e., sand buried depth, SPT counts, seismic shaking intensity. A complete and objective acquaintance of liquefaction in Christchurch earthquake is obtained while the liquefaction characters and relevant correlations are compared with those from other regions and countries.