Fly-Ash Slurry Island: I. Theoretical and Experimental Investigations

In construction of a man-made island using a cofferdam and fill, problems are often encountered, such as sliding failures of a soft seabed or ruptures of the cofferdam. A new filling method, underwater placement of a light and self-hardening slurry, presents great advantages that are confirmed by theoretical analysis. An appropriate slurry for this new method, containing fly ash, volcanic ash, and a small amount of cement, is developed from experimental investigations. This light, self-hardening slurry greatly reduces the earth pressure and increases the safety factor of the island, and it also makes subsequent construction work easier. Strength development of the slurry is inhibited by low temperature, but this can be compensated for by a small increase in the cement content. Practical slurry compositions are also proposed based on laboratory studies, which included test-tank tests. It is concluded that underwater placement of fly-ash slurry is a viable method for man-made island construction.