A precompression method of soft ground improvement using dewatering

Abstract

The background and geology of the Tokyo Bay area of Japan, and recent soil improvement methods used in Japan are described. The vertical drain method has frequently been used to improve thick quarternary deposits in this area. This paper describes a case history of a dewatering method in combination with the vertical drains and preloading in a major soft ground improvement project in the Urayasu area of the Tokyo Bay. The dewatering method is a vacuum consolidation method, which is tentatively applied to the soft clay ground.In the combined dewatering method, the waterhead in a vertical sand drain is lowered by pumping the water from a sand layer within or below a soft clayey layer using deep wells. The dewatering applies negative water pressure to the soft clayey layer, promoting its consolidation.The authors confirm the consolidation effect of the dewatering and establish the applicability of the combined dewatering method to the soft clay ground.It is concluded that the dewatering method described significantly increases the shear strength and the consolidation yield stress of the soft clayey layer. BACKGROUND OF TOKYO BAY AREA