Properties And Applicability of Filling Material For Compaction Pile Method

The sand compaction pile (SCP) method has been widely used as ground improvement method in Japan. It conforms with fundamental principles of compaction and consolidation drainage. As a result, it has been used successfully on many occasions for the improvement of all types of soft grounds (ranging from sandy to clayey ground), using natural clean sands as filling material. In order to lessen the environmental impact through efficient recycling of construction surplus soils and by reduced use of natural sands an improved SCP method was developed, in which construction surplus soils and coal ashes are used as a substitute for sands used as filling material in conventional SCP method, so as not to exhaust sand resources. Originally, the method have been developed for clayey ground, in which plastic board drains located around piles were substituted for drainage, and in the design the strength increase of soft clay due to dissipation of excess pore water pressure generated through installation of sand compaction piles was newly considered. As for sandy ground, as the compaction effect is not significantly affected by filling material, this method has been acknowledged to be effective against liquefaction. However, as these filling material have different properties from clean sands, it is very important to clarify the material properties for compaction pile methods. In this paper, some laboratory tests (triaxial tests, permeability tests etc.) were conducted to investigate these material properties. Then, the test results were discussed from the view point of material properties applicable to compaction pile methods. Furthermore, outline of this method and several field applications were shown. Finally, it was concludes that this method made effective use of construction surplus soils which had to be disposed of in most cases,