Research on the Densification of Vibroflotation against Liquefaction for Filling Coral Sand

Coral sand is the main filling material for artificial island offshore, which is generally a wide-graded soil composed of sand particle and gravel particle. It has the characteristics of irregular edges and corners, high compressibility, rich internal and external pores, and easy breakage. Based on historical seismic damage data investigation, the peak seismic acceleration of coral reef sand liquefaction surface rang 0.1g~0.4g. Therefore, anti-liquefaction treatment should be considered for coral reef sand site located in strong earthquake zone. Based on the Timor-Leste Tibar Port Project, a comparative analysis of the influence of densification of vibro-flotation against coral sand liquefaction when applying different quality control measures and design spacing. The obtained result is as follow: for the loosely dredged coral reef sand layer with high fine particle content, when adopt the 3.5m spacing for treatment, adding re-penetration process and increasing the vibration time during compaction stage would increase the degree of compaction significantly, whereas the effect of further reducing the spacing is limited. For clean medium-dense filled coral reef sands, when the 3.5m vibro-impact spacing is adopted, adding re-penetration process and decreasing the spacing during the compaction stage, the compactness can be greatly improved. For the surface filled coral reef sand, the compaction effect is normally poor after vibro compaction, and additional strengthening measures should be taken, such as watering to increase the water table of surface layer before vibration, rolling compaction after vibration, etc.