DEVELOPMENT OF EVALUATION METHOD FOR LIQUEFACTION OF GROUND CONSIDERING DUCTILE NATURE

现有的液化预测方法对是否存在液化破坏给出的是一种可供选择的结论。但是，根据神户大地震等实际的液化破坏，很明显，破坏程度不断变化。这是因为地震运动作为外力的荷载水平和地基的韧性不断变化。特别是对土的韧性，目前还没有定量评价的方法。因此，我们不能区分刚性恢复的密实桑迪和没有韧性的松散砂土的断裂事件。本研究的目的是发展能够定量评价土的延性的技术，1998财政年度提出了能够定量评价土的延性的新的应变控制试验方法。基于该技术，研究了除砾石外由含砂量和细粒级组成的各种土壤的适用性。对试验结果进行了塑性应变能的研究，结果表明塑性应变能成为反映土的延性指标的指标。1999年度提出了地震烈度作为外力与强度指标成比例的评价技术。即提出了在一定地震动输入下，用于地面塑性变形的能量的预测方法，并在2000年财政年度公布了研究结果。本研究成果已在国内外学术期刊和国际会议上发表。此外，研究报告作为科学研究报告的补助金印刷，并分发给同一领域的研究人员。

Current prediction method of liquefaction issues the alternative conclusion of whether there is no liquefaction damage. However, according to the actual liquefaction damage such as the Great Hanshin Earthquake, it is clear that the damage level continuously changed. This is because load level of the earthquake motion as an external force and the toughness of the ground continuously change. Especially, there is no technique that quantitatively evaluates it on the toughness of the soil in present state. Therefore, we can not distinguish the fracture event between of dense sandy soil in which the rigidity recovers and of the loose sand without ductile nature. The purpose of this study is to develop the technique that can quantitatively evaluate ductile nature of the soil.New strain controlled-test method that could quantitatively evaluate ductility of the soil was proposed in the 1998 fiscal year. Based on this proposed technique, the applicability was examined for various soil composed of sand content and fine-grain fraction except for gravel. The experimental result was studied in plastic strain energy, and it showed becoming an index which shows ductility index of the soil.The evaluation technique of earthquake intensity as an external force in proportion to the strength index proposed in the 1999 fiscal year. That is to say, the prediction procedure of energy amount used for the plastication of the ground was proposed, when some earthquake motion input it.The research result was presented in the 2000 fiscal year. And the result of this study was published in academic journal and international conference of domestic and overseas. In addition, the research report was printed as a grant-in-aids for Scientific Research report, and it was distributed to the researcher of the same field.