Laboratory Studies on the Characteristics of Public Fill used in Reclamation Project in the Deep-sea Area

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To reduce solid wastes and recover useful resources, an artificial island in the deep-sea area was built and it was planned to use the sorted public fill as the replacement of sand in the land reclamation. The use of the public fill as the replacement of sand not only reduced the CO2 emission, but also shortened the construction period. Although the use of public fill gives benefits to environmental sustainability, the public fill is rarely used in Hong Kong for reclamation in the deep-sea artificial island. Furthermore, the short-term and long-term post-construction settlement due to surcharge load is a key issue in the reclamation work, while limited information of the physical and mechanical properties of the public fill could be found in the past engineering projects. In addition, there are many uncertainties and influencing factors in the construction site such as the surcharge load magnitudes, modes of the loading process, and the variability of geotechnical parameters. How these factors influence the mechanical behavior of the public fill is an interesting issue. This paper gives first-hand laboratory test results accompanied by theoretical analysis to address the mentioned issues. After a comprehensive and careful measurement of several basic engineering properties, such as bulk density, particle size distribution, and Atterberg limits, large-scale oedometer tests were systematically conducted to study the compressibility of the public fill. It is found both volume compressibility and consolidation coefficient decrease with an increasing axial effective stress. An interesting finding is that an increasing fines content with a certain range will lead to an increase in the compressibility of the public fill, indicating the fines content may need to be considered in the land reclamation works. In addition, remarkable creep could be observed if the current vertical stress is lower than the preloading pressure. After obtaining design parameters and ensuring allowable settlement through both in-house laboratory tests and in-situ field tests, the project in the technical paper may be a good reference for future land reclamation design and construction cases.