Abstract: The sand liquefaction problem has been one of the important topics in soil dynamics and geotechnical earthquake engineering. Based on a project of the Middle Route of South-to-North Water Transfer, physico-mechanical parameters of soil have been obtained through field and laboratory tests. And the dynamic numerical analysis on the liquefied sand foundation of the main canal which has been reinforced by compacted gravel piles is conducted with FLAC3D. The results show that, for the drainage of the compacted gravel piles, the excess pore water pressure and pore pressure ratio in the saturated sand foundation of the main canal bottom have been significantly reduced compared to ones before reinforcement. Monitoring curves of the saturated sand in the bottom of the main canal show that, with the duration of the seismic loading, the peak values of the excess pore water pressure and pore pressure ratio in the saturated sand foundation decrease significantly compared to ones before reinforcement; and the time-history curve declines quickly when to the peak value, which keeps essentially unchanged before reinforcement. For the drainage and compaction effect of the compacted gravel piles, the liquefaction of the sand layers, in the bottom of the main canal, and from the outside platform of the embankment to the bottom of the slope foot, is eliminated effectively. And no liquefaction occurs in the saturated sand foundation of the main canal bottom after reinforcement.

Key words: compacted gravel pile, liquefiable sand soil, dynamic numerical analysis, excess pore water pressure, pore pressure ratio