3D liquefaction analysis of block scale

In recent years, for the purpose of assuming earthquake damage to an entire city and traffic network and considering countermeasures, the seismic response for the wide area of a city block and city scale has been attempted. To obtain a seismic response close to the actual response, it is necessary to consider the 3D effect caused by stratal organization and liquefaction of the ground. Therefore, our company conducted the 3D liquefaction analysis of a block scale for cities located on the alluvial plains of the Kanto area. As a result, we confirmed that it was possible to perceive in terms of area the tendency of the natural vibration frequency of the ground by observing the area under consideration, and the 3D analysis provided nearly the same response as that of the 2D analysis in a place where the 2D plane strain could be assumed.

Shaking of liquefied ground can be assessed by numerical analysis. Our company has uniquely parallelized the liquefaction analysis program (FLIP3D) to realize large-scale calculations. In the analysis in which part of an urban area of 2 km x 1.5 km is modeled (approximately two million nodes), we confirmed that the calculation results were correct with respect to some viewpoints. This technique can be applied to a detailed liquefaction assessment of a wide area of ground.