The new Hong Kong airport at Chek Lap Kok is being constructed on a 1248 hectare site of which 928 hectares is reclaimed land. Part of the reclamation consists of marine sand fill. Site investigation, including the CPT and shear wave velocity testing, indicated that the sand was in a relatively loose state state below the water table, with relative densities in the order of 20 to 40%. Vibrocompaction was carried out at three different areas of the reclamation in order to increase the reiative density of sand fill, thereby increasing its’ stiffness and strength, and creating an improved and more uniform material for follow on construction.
The method for acceptance testing for the vibrocompaction was based on the use of the CPT, with the acceptance criterion set as a tip resistance value of either 8 MPa or 15 MPa, depending on required degree of compaction.
This paper presents the results of the vibrocompaction and discusses some of the factors encountered during the compaction that can lead to apparent non-conformance with the specification. Conclusions are drawn from the work with recommendations that should be considered for future vibrocompaction works. A knowledge of the initial state of the sand including index properties, relative density and compressibility, is important when selecting an acceptance criterion. An inappropriate acceptance criterion may cause unnecessary delays of the work and increased costs as a result. The use of shear wave velocity measurements as a compliment to the CPT testing is also discussed as valuable information on the state of the sand can be derived from this method of testing.
