Appropriate measures to prevent the liquefaction-induced inclination of existing houses

Abstract

Many wooden houses settled and tilted due to liquefaction during many past earthquakes. In greatly tilted houses, inhabitants felt giddy, sick and nauseous, and found it difficult to live in their houses after the earthquakes. According to a new standard announced by the Japanese Cabinet after the Great East Japan Earthquake, houses tilted at angles of more than 50/1000, of 50/1000 to 16.7/1000, and of 16.7/1000 to 10/1000 were judged to be totally collapsed, large-scale half collapsed and half collapsed houses, respectively. According to the authors’ previous study on the inclination of houses, several factors affect inclination. Among them, the effect of adjacent houses was dominant during past earthquakes in residential areas. If two houses are close to each other, they tilt inward toward each other, and if four houses are close, they tilt toward their common center. The authors conducted several analyses to develop appropriate measures to prevent the liquefaction-induced inclination of existing houses. The liquefaction-induced deformation of structures can be estimated by empirical methods, static analyses (residual deformation method), and dynamic analyses. In this study, a static method called ALID was used because this method is simpler than dynamic analyses. Analyses were conducted for two possible countermeasures. One countermeasure is to lower the ground water table by placing drain pipes or shallow wells under roads. ALID analysis results showed that inclination decreases when the ground water table is lowered