Abstract
In Osaka City the vertical drain method has been used to promote consolidation and settlement of clay soils (alluvial clay and dredged clay layers), and two new techniques have been developed, based on the principle of reducing neutral stress, with the specific purpose of reducing the volume of dredged soils. One technique combines the dewatering method with the newly developed plastic board drain by floating (PDF) method, and the other combines the PDF method with a vacuum consolidation method in which dredged clay is used as a sealing material over the top of horizontal drains.
This paper gives an outline of the latter technique (accelerated consolidation method combining vacuum consolidation and PDF methods) and its major feature, and the results of field observations obtained from test and actual implementations. Actual settlement after implementation, taken from the field observations, conformed closely with calculated values, confirming that this technique promotes settlement at landfill sites where landfill is ongoing, in other words they are extremely effective as methods to reduce the volume of dredged clay soils. Furthermore the passage volume and capacity of water through drain materials are also studied.
