The invention discloses an existing
cutting broadening roadbed structure in a
karst area. The structure comprises a
basement karst cave area and a
basement non-
karst cave area. The
basement karst cavearea is provided with long piles and short piles, the basement non-karst
cave area is provided with short piles, the bottoms of the long piles are arranged in a stable stratum below the basement karst cave area, light replacement bodies are arranged on the tops of the long piles and the tops of the short piles and filled with soil fillers, and drainage ditches are formed in two sides of the lightreplacement bodies. The light
soil material is low in density and high in
pressure resistance, so that the additional stress for widening the roadbed is reduced; the light replacement body can improve the
structural integrity, enables the load of an upper structure to be smoothly transmitted to the lower long
pile and the lower short
pile, so that the eccentric force is avoided; the load of an upper roadbed, a rail and a
train is carried effectively, an equal-load replacement effect is realized, the additional stress acting on a karst cave top plate is reduced effectively, and deformation anddamage are avoided. On the basis of the structure, upward arching of an existing
cutting caused by grouting can be avoided, and
safe operation of a high-speed
train is guaranteed; the structure is low in
engineering cost, and
engineering investment is effectively controlled.