Study on the allowable deformation of structures in liquefied grounds and appropriate measures against liquefaction

液化引起建筑物的变形，如建筑物的沉降和人孔的浮起。然而，在目前的液化设计程序中，仅对液化的发生进行判断。没有对结构的变形进行评估。在1995年小谷县南部地震后新设计规范中引入的2级地震运动设计中，由于现有的许多措施不能防止液化的发生，因此有必要对变形进行评估。在此基础上，通过多次现场调查、振动台试验和残余变形分析，研究了液化地基结构变形和允许变形的适宜评价方法。提出了防止房屋沉降和管道浮沉的简易措施。通过振动台试验和地震反应分析，验证了该方法的有效性。研究得出的主要结论如下：1。对2000年鸟鸟县-西武地震中临时房屋液化沉降的现场调查表明，其允许倾斜角度几乎为1/100.2。残余变形分析（ALID）可用于评价储罐的沉降和埋地管道的浮沉。通过这种分析，还评价了夯实地基改良的有效性。在2级地震作用下，即使改良地基发生液化，也可以通过关注结构沉降来评价碎石排水方法的有效性。通过在埋地管道上加贴标签的方法，可以有效地防止液化引起的浮力。在2003年的枥木地震中，许多污水井口漂浮起来。详细的现场调查表明，浮力是由回填土液化引起的。

Liquefaction causes deformation of structures such as settlement of buildings and floatation of manholes. In current design procedure for liquefaction, however, the occurrence of liquefaction is judged only. Deformation of the structures is not evaluated. In the design for Level 2 earthquake motion, which has been introduced recently in new design codes after the 1995 Hyogoken-nambu earthquake, it is necessary to evaluate the deformation because many current countermeasures can not prevent the occurrence of liquefaction. Then, in this research, appropriate evaluation methods for liquefaction-induced deformation of structures and allowable deformation in liquefied grounds were studied by conducting several site investigations, shaking table tests and residual deformation analyses. Simple measure methods against the settlement of houses and the floatation of conduits were developed also. Effectiveness of the developed methods were confirmed by carrying out shaking table testes and seismic response analyses. Main conclusions derived from the research were as follows :1.A site investigation on the liquefaction-induced settlement of timer houses during the 2000 Tottoriken-seibu earthquake showed that the allowable angle of tilting was almost 1/100.2.Settlement of tanks and floatation of buried conduits can be evaluated by a residual deformation analysis "ALID." Effectiveness of ground improvement by compaction was also evaluated by this analysis.3.Effectiveness of gravel drain method can be evaluated by focusing on the settlement of structures even though the improved ground is liquefied under Level 2 earthquake motion.4.A simple countermeasure method by attaching brads to buried conduits was effective to prevent liquefaction-induced floatation.5.A lot of sewage manholes floated up during the 2003 Tokachi-oki earthquake. Detailed site investigation revealed that the floatation induced due to the liquefaction of backfilled soils.