A waste disposal site to be constructed in a coastal area is generally surrounded by seawall structures to accommodate waste reclaimed. In case that the seawalls are required to prevent substances contained in waste from leaking out to the sea, they are constructed as quasi-impermeable structures. The quasi-impermeability of the structures is required to be retained by self-sealing performance even in their deformed conditions to be possibly caused by deformation of soft ground or actions of earthquake, wave, tide etc. In addition, it is preferable for quasi-impermeable material to have the features of long durability and adjustability in its fabrication to suit for various construction conditions. We have developed a new quasi-impermeable material with the features of self-sealing, long durability and adjustability in its fabrication by main use of dredged marine clay taking advantage of its low impermeability. In the relevant standard of ministerial ordinance, quasi-impermeable seawall structures are required to have the thickness of 0.5m or more and equivalent hydraulic conductivity of 1.0×10−8 m/s or less. In this study, proposed is a quasi-impermeable seawall structure with steel frame by jointing H-steel sheet piles and such clayey quasi-impermeable material filled inside the frame. The overall performance of the proposed structure was examined in a field test exposing it to a natural sea condition for more than one year. The self-sealing performance of the structure was also examined in the test after intentionally deforming it. Regarding the quality of filling clayey material, the homogeneity of filling was investigated by sounding and sampling tests. It has been confirmed that the structure realizes quasi-impermeability with equivalent hydraulic conductivity of the order of ke = 10−9 m/s, which satisfies the design criteria prescribed by a ministerial ordinance in Japan to allow for practical use in the sea.

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