Field Placing Test of Lightweight Treated Soil under Seawater in Kumamoto Port

Abstract

A lightweight treated soil method has recently been developed to reuse dredged soils as artificial lightweight geomaterials, the density of which ranges from 1.0 ~ 1.2 g/cm3, for coastal construction projects. In the two types of lightweight soils, foam-treated soil (FTS) and bead-treated soil (BTS), the slurry of dredged soil is mixed with cement and air foam, or cement and EPS beads (the diameters are 1 ~ 3 mm), respectively. The lightweight treated soil method have been applied in several seaports and coastal airport projects, but only in the sites at a level shallower than –3 m to avoid density change due to large water pressure and the possibility of washout during underwater placing. In this study, full scale field placing tests of lightweight soils were carried out at sites 10 m below the sea level in Kumamoto Port with the purpose of investigating the material properties of lightweight soils placed under deep water. Especially the change of density through the process of mixing, transportation, placing and hardening was examined in detail. It was found that the lightweight soil method can be applied under sea water of –10 m, although a part of the total volume of mixed foam or mixed EPS beads is swept away during the construction process. However the wet-density of lightweight soil measured 1 year after the construction was almost the same as that of a 28-day specimen, while the 1 year strength was 40% larger than the 28-day strength.