Densification of Land Reclamation Sands by Deep Vibratory Compaction Techniques

Loose granular sand deposits formed during the land reclamation process are vulnerable to liquefaction upon imparting seismic forces. These loose granular sand fills could encounter bearing failures or compress beyond tolerable limits under static and dynamic loads. In order to eliminate such failures, loose granular soils require densification to enhance their engineering properties. Deep compaction is the only means to improve these thick deposits of loose sandfill in many foreshore land reclamation projects. Muller Resonance Compaction (MRC) and vibroflotation are deep vibratory compaction techniques, which are suitable to densify thick layers of loose granular fills. This paper describes the applications of deep compaction vibratory techniques in a mega-land reclamation project in the Republic of Singapore where the efficacy of densification was verified by Cone Penetration Tests (CPT) undertaken in a Pilot Test Area. The top sand layer of about 1.5 to 6.0 meters is in the medium to dense state and dilates during shear. In the MRC technique, high vibrating energies are used, which results in the whole mass of soil being rearranged, but a weak point was found at the location of the probing point. In vibroflotation, the densified column of soil was found to form at and surrounding the probe point and the density of the granular soil reduced with distance from the probe point. The aging effect in vibroflotation was found to be significant. vibroflotation was found to have several advantages compared to the MRC technique. Due to the excess water in the pore spaces caused by the high pressure jetting in vibroflotation, the water pressure dissipation further enhances the densification due to the aging effect.