Depth distribution of liquefaction strength characteristics at a site damaged by the Great East Japan Earthquake and predictions of liquefaction

摘要

In the Great East Japan Earthquake, the reclaimed land in Tokyo bay was damaged by liquefaction. In this study, a detailed ground investigation is conducted to clarify the damage mechanism by subsidence and inclination of detached houses due to liquefaction in Irifune 4—chome, Urayasu city, which suffered major damage after the earthquake disaster. The investigation included conducting questionnaire surveys on liquefaction damage, determining the N-value by using a standard penetration test, PS logging, groundwater level measurements, and laboratory tests for undisturbed samples that were collected continuously. This study describes; 1) the depth distribution of the liquefaction strength ratio obtained from continuously collected undisturbed samples, 2) the characteristics of each depth, and 3) the energy characteristics of each specimen. The characteristics of each method were then evaluated by comparing various liquefaction predictions (i.e., effective stress, stress based method (F _(L) method), energy method). In the results of liquefaction prediction, the rise process of excess pore water pressure by the effective stress analysis was almost entirely consistent with the eyewitness testimony of the in habitants. A difference in the evaluation result between F _(L) method and energy method was noted; in the F _(L) method, the F _(L) value decreases with depth, whereas in the energy method, it tends to liquefy easily with shallower depths.