The　increasing　frequency　of　extreme　rainfall　is　leading　to　a　rise　in　groundwater　levels　in　coastal　areas,　significantly　affecting　high-speed　railway　operations.　To　address　this　concern,　this　study　developed　a　2.5-dimensional　finite　element　model　of　a　coupled　track-embankment-ground　system　based　on　Biot’s　porous　media　theory　to　analyze　the　effect　of　groundwater　level　rise　on　the　critical　velocity　of　high-speed　railways　and　vibration　responses.　The　findings　reveal　a　consistent　decrease　in　the　critical　velocity　of　high-speed　railways　with　rising　groundwater　levels.　Particularly,　the　increase　in　groundwater　levels　within　the　embankment　significantly　influences　the　critical　velocity　compared　to　a　similar　rise　in　the　foundation’s　groundwater　level.　Furthermore,　deformations　induced　by　passing　trains　significantly　increase　as　groundwater　levels　rise.　Specifically,　when　the　groundwater　level　rises　from　the　foundation　bottom　to　the　subgrade　surface,　subgrade　surface　deformation　increases　by　approximately　55%.　As　trains　approach　the　critical　velocity,　significant　vibration　phenomena,　known　as　the　＇Mach　effect,＇　occur　at　the　foundation　surface.　Importantly,　as　groundwater　levels　rise,　the　＇Mach　effect＇　intensifies.　Analyzing　the　vibrating　frequency　spectrum　of　the　displacement　response　demonstrates　a　substantial　increase　in　vibration　amplitude,　particularly　in　the　high-frequency　region,　as　groundwater　levels　rise.　This　study　highlights　that　the　rise　in　groundwater　level　not　only　amplifies　vibrations　but　also　extends　the　propagation　of　high-frequency　vibrations,　underscoring　the　importance　of　effective　embankment　waterproofing　in　controlling　track　vibrations.　©　2023　by　the　authors.