Design of Grid-Wall Soil Improvement To Mitigate Soil Liquefaction Damage in Residential Areas

Abstract eng:
In the land reclamation areas of Urayasu city, 8,700 small buildings such as residential houses suffered severe damage due to liquefaction during the 2011 Tohoku earthquake. This represents almost one third of all houses in Japan that suffered severe damage due to liquefaction. Following this event, Urayasu city adopted grid-wall soil improvements as countermeasures to mitigate liquefaction. Investigations and design processes are ongoing for 4,103 residential houses, and the construction stage started in January 2016 for 44 residential houses. For the conditions of simplified grid-wall soil improvement design, the spacing between the grid-walls is restricted within L/H = 0.8. L is the spacing between the gridwalls and H is the thickness of the liquefaction layer. However it is difficult to adopt L/H as a design guideline because the grid-wall soil improvement has to be applied under existing houses. The construction of grid-walls directly under houses is impossible. Consequently, the spacing between the grid-walls increases. It is suitable to use the settlement of a house as a design guideline for the conditions in Urayasu. The finite element method with a quasi-three-dimensional analysis model can be used to estimate the settlement of houses. However, there are no examples that have adopted the settlement as a design guideline in grid-wall soil improvement design. As such, dynamic centrifuge model tests were conducted to investigate the relationship between the settlement of houses and the grid-area. The design method and numerical analysis was verified through the experiments.

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