The nature of sand is fundamentally that of a discrete granular system, and its liquefaction process involves the intricate interplay of multi-scale and coupled field effects. The open-source SPH solver is employed for the development of a fluid-solid coupling calculation module, and this approach is utilized to reproduce the liquefaction responses in saturated sandy sites at macro and meso scales and to investigate the liquefaction mitigation performance of gravel piles. The study shows that under surface drainage conditions, liquefaction occurs almost simultaneously at all depths, with the excess pore pressure ratio reaching 1.0. Under dynamic loading, the normalized average coupling force of particles initially increases slowly, then quickly rises to 1.0 at the onset of liquefaction, and subsequently decreases progressively from deeper to shallower layers. Simulations of gravel piles demonstrate that under dynamic loading, the excess pore pressure ratio is only 0.6. Pore fluid in the fine sand flows towards the gravel drainage channels, reducing the accumulation of excess pore pressure and significantly enhancing soil strength, thus providing effective liquefaction resistance.