Study on the rational design method for treating area against liquefaction based on performance-based design

1995年小古根南部地震后，提出了基于1级地震运动和2级地震运动两种地面运动进行抗震设计的建议。在2级地震运动下，目前的对策无法阻止液化。因此，有必要引入一种新的设计理念，不是基于液化的发生，而是基于结构可能受到的破坏程度。这种新的设计理念，即所谓的基于性能的设计，必须是合理的，并将用于改善抗液化面积的设计。在此基础上，通过多次振动台试验、循环扭剪试验和分析，研究了基于性能设计的液化处理区域合理设计方法。在振动台试验中，使用了一个模型屋和松散的沙质地面。样板房下面的一些区域通过致密化得到了改善。在改进区域的不同深度和宽度下进行了振动台试验。随着改善区深度和宽度的增加，样板房的液化沉降减小。在分析中，使用了作者自己开发的代码ALID。对几个改进领域也进行了分析。改善面积的效果也得到了类似的结果。分析认为，现有的液化处理区设计方法存在较大的高估，基于性能的液化处理区设计方法可为合理设计液化处理区提供依据。

After the 1995 Hyogoken-nambu earthquake, it suggested basing earthquake-resistant design on two types of ground motion : Level 1 earthquake motion and Level 2 earthquake motion. Liquefaction cannot be prevented by current countermeasures under the Level 2 earthquake motion. Therefore, it is necessary to introduce a new design concept based not on the occurrence of liquefaction but on the likely degree of damage to structures. This new design concept, so called performance-based design, must be rational and will be used for the design for improving area against liquefaction.Then, a study on the rational design method for treating area against liquefaction based on performance-based design, was conducted by many shaking table tests, cyclic torsional shear tests and analyses. In the shaking table tests, a model house and loose sandy ground was used. Some area under the model house was improved by densification. The shaking table tests were carried out under several depth and width of the improved area. Liquefaction-induced settlement of the model house decreased with the increase of the depth and/or width of the improved area. In the analyses, a code named ALID, which has been developed by the author, was used. Analyses were carried out under several improving areas also. Similar results on the effect of improving area were obtained. Then it was concluded that the current design method for the improving area is overestimated, and the performance-based design method is useful for rational design of treating area against liquefaction.