Airfoam-treated lightweight soil is lightweight and provides for the early age development of shear strength and effective utilisation of dredged soils. This paper summarises a 10 year follow-up study of the lightweight soils that were placed as backfill at the seawall in Kobe Port Island and Tokyo International airport. These two sites are the early case examples of constructions undertaken in 1996 including the recovery project after the Kobe earthquake disaster and the offshore expansion project of the Tokyo International airport. Sampling and laboratory testing were carried out to investigate the physical and mechanical properties in order to compare the initial material condition. The depth profiles of the soil parameters such as bulk density, water content, pH, calcium content, shear strength, needle penetration resistance, compressive yield stress and compression index were examined. Consequently, it was confirmed that the physical and mechanical properties of the airfoam-treated lightweight soil satisfied their required performance criteria, indicating that the lightweight soil had sufficient durability for use as geomaterial for construction in coastal areas.
Recently, a shortage of soil disposal area has been serious in Japan, and there has been a demand to dispose the dredged soil as much as possible in the disposal area with limited capacity. To meet this demand, the vacuum consolidation method with horizontal prefabricated drains has been applied to the soft ground formed by dumping of dredged soil. Horizontal drains of 100cm wide, 10mm thick and 117-171m long were installed at the horizontal interval of 0.8m on the bottom surface and a middle section of the disposal area. Then, soft soil was improved by the vacuum pressure of over 75-80kN/m 2. The volume of dredged soil converted in the original sedimentation condition was 1.1 times as much as the capacity of the disposal area, though all of the dredged soil was successfully accepted in the disposal area because of bulk reduction of the soil by the vacuum consolidation method.
The dredged soil dumped into a reclamation facility is generally heterogeneous. If the reclamation is executed using hydraulic transportation through pipes, large particles will be deposited around their outlets, and fine particles will be deposited apart from those outlets, resulting in significant grain size segregation. Therefore, ground improvement by applying a preload or vacuum to the dredged soil deposit with prefabricated vertical drains (PVDs) may result in an unexpected differential settlement. In the present study, partial sandy layers in a dredged soil deposit were identified as three-dimensional information using the penetration resistance of the mandrel in the PVD installation, which was recorded as dense information for a wide region. It was clarified that the depth profile of the penetration resistance of the mandrel in the PVD installation was useful for investigating the soil stratigraphy, because it is closely related to the depth profile of the tip resistance in cone penetration tests (CPTU). The relative penetration resistance, defined as the penetration resistance eliminating the data trend that reflects the effects of the overburden stress, shear strength, sleeve friction and buoyance, is useful for identifying the partial sandy layers in a dredged soil deposit. A classification equation was proposed for identifying the partial sandy layers. Firstly, the depth profile without the sandy layer was approximated, and then the threshold value of 1.0 MN/m 2 was used to identify the partial sandy layer. To verify the availability of this proposed method, the depth profiles were compared with the results of CPTU tests. In addition, the predicted settlement, calculated on the basis of the stratigraphy obtained using the penetration resistance of the PVDs, was compared with the ground surface profile leveled after vacuum consolidation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.