The integrated projects for soil improvement have been planned in many municipalities in and around the Tokyo Metropolitan area where residential lands have been constructed in young reclaimed islands or in former river channels and swamps. The issues to be considered in the projects are as what follows:
There are many houses on the ground surface and they cannot be demolished or removed for soil improvement.
Therefore, soil has to be improved under existing houses.
Hence, densification is not possible because big machines cannot come in and also because the induced soil deformation is not allowed by fragile houses.
Grouting is too expensive for people, although it can be executed under existing houses.
The public sectors do not want to recommend to people those new technologies that have not been validated.
Consequently, only two choices have been chosen as the candidate soil improvements, which are ground water lowering in most municipalities and square grids of underground walls in Urayasu City.
Ground water lowering was executed in Amagasaki City near Osaka after the 1995 Kobe earthquake, while the same earthquake proved the reliability of the underground grid wall in Kobe Harbor.
Ground water lowering produces unsaturated and unliquefiable soil crust at the surface, while underground grid walls constrain cyclic shear deformation of soil to reduce the excess pore water pressure.