Abstract: The main experiences obtained by the authors since 1984 in improvement of liquefiable saturated silty foundations with vibro-compaction gravel piles on three construction sites located in high seismic intensity zone are introduced in this paper. The results of the investigation have shown that good improvement effect and great economic benefit can be achieved using vibro-compaction gravel pile to improve the liquefiable foundations, especially the liquefiable silty foundations. The general methods used for evaluating, the liquefaction-inhibiting effect of complex foundation are discussed. A simplified method for evaluating liquefaction-inhibiting effect of complex foundation in short time is presented and has been used tentatively in practical engineering.