Preliminary Study On An In-situ Liquefaction Test Under Artificial Dynamic Loading

Soil liquefaction is a major factor to cause damages in earthquakes, and induces a great loss of lives and properties. Liquefaction is one of the most important topics in geotechnical earthquake engineering. Its devastating effects sprang to the attention of geotechnical engineers and researchers in 1964. Since then, liquefaction has been studied extensively by hundreds of researchers throughout the world. Although much progress has been made over the past four decades, liquefaction, because of its complexity, remains an important branch of future research both in theoretical and engineering practice fields.Laboratory test, which is an important approach in liquefaction research, has many intrinsic limitations. Those make laboratory test results be different from responses in actual liquefied sites. An approach that it in-situ monitors the responses of soil deposits under seismic loading was applied in liquefaction research in1970s around the world. However, because of rare occurrence of earthquakes and immaturity in short-term forecast technology, few records have been reported.As an effective way to overcome many disadvantages and limitations existing in current testing techniques, in-situ liquefaction test under artificial dynamic loading has been developed. The in-situ dynamic liquefaction test provides a new alternative approach to evaluate the liquefaction susceptibility of soil deposits, and advance the state of knowledge in pore water pressure generation and liquefaction mechanism in real liquefied sites. Moreover, it can also be used to study other issues in the field of geotechnical earthquake engineering, and open a window to study dynamic properties of soil. Its potential applications and advantages need be explored and developed in the future. At present, this technique has developed at a certain extent at abroad, but it remains in the exploring stage and no generally applicable method has been proposed. Furthermore, the research has just started in China mainland.Based on the summary of the-state-of-art on in-situ liquefaction dynamic tests at home and overseas, a technology platform of the in-situ dynamic liquefaction test under artificial loading has been established. Moreover, investigations on special liquefaction problems have been done by this approach. The main salient points and achievements in this dissertation are as follows:1. A technology platform of in-situ dynamic liquefaction test has been established. Through field vibration test and data analysis, the feasibility of this testing technique has been verified. Also, the procedures and preparation of the in-situ liquefaction test are presented. An exclusive in-situ liquefaction testing technique under artificial dynamic loading has been developed.2. Two types of the in-situ dynamic liquefaction test, through a model box or test pit, are designed and accomplished. Moreover, its advantages and characteristics are discussed. The test results and data analysis demonstrate satisfactory credibility and operability of the two in-situ liquefaction tests. Also, some problems existing in the test are pinpointed, which can pave the path for further studies on geotechnical in-situ testing techniques under artificial dynamic loading.3. By the in-situ dynamic liquefaction test, the quantitative relationships between excess pore water pressure and the amplitudes of surface soil acceleration, shear strain are obtained when the soil is liquefied. Also, some factors to influent these relationships are analyzed and elucidated.