 Installation of ground water lowe

 Installation of ground water lowering mechanism is much less expensive than construction of grid walls, although it needs maintenance cost of pumps and electricity.
Urayasu City chose the more expensive grid walls because there is a very thick soft clay layer under liquefaction-prone sand and it was feared that consolidation settlement may be reactivated by the lowered ground water level. Certainly, construction of underground walls requires further efforts to reduce the cost, while maintaining the seismic performance.