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

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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.