| Sand boils and water gushing due to liquefaction occurred in extended areas of reclamation grounds in the northern part of the Tokyo Bay and the downstream section of the Tone River in the Great East Japan earthquake. Especially in the northern part of the Tokyo Bay amount of boiled sand and gushing water interfered with the lives of residents and many private houses, sewage manholes, pipes and etc. were damaged due to liquefaction (JGS 2011, etc).The damage was mainly caused on the east side of the northern part of the Tokyo Bay, Chiba prefecture. Areas where liquefaction occurred in the earthquake are limited to mainly reclaimed land.In other hand, areas where liquefaction occurred in the west side of the northern part of the Tokyo Bay, Tokyo Metropolitan, were quite smaller than the east side, although reclamation works have been conducted after the 16th century in the west side. These areas were limited the reclaimed land beside the coast.A point in common between the reclaimed land where liquefaction was observed in the east and in the west was recently reclaimed land after the Showa era (after 1926). Therefore, it is pointed out that young grounds are likely to have a smaller resistance against liquefaction and, old grounds and natural grounds are likely to have a stronger resistance.Koseki and Ohta (2001) reported that liquefaction resistance is influenced by the aging of the sample based on element tests. But, the mechanism of improvement of liquefaction resistance due to aging has not been clarified sufficiently.In this research amount of data on boring conducted in Kanto region was collected, and relationships between occurring of liquefaction in the earthquake and SPT N-values were organized. In addition, a map showing distribution of thickness of liquefiable sandy soil created in order to be applied to future investigation will be introduced. |
