Reinforcing method for terrace loess foundation and built variable-rigidity composite pile composite foundation

The invention discloses a reinforcing method for a terrace loess foundation and a built variable-rigidity composite pile composite foundation. The reinforcing method comprises the steps that an area needing to be reinforced is leveled, and shallow pits are dug; upper-layer holes are generated, lower-layer holes are drilled according to the water content of a loess layer below an A layer, and pile holes are formed; rigid pile material mixtures are poured and vibrated, then flexible pile material mixtures are filled, layered tamping is carried out till the pile holes are filled, and variable-rigidity composite piles are built; the second variable-rigidity composite pile is built; all the variable-rigidity composite piles are built in the reinforced area; bulk materials are laid in the shallow pits; and after cement is fully hardened, the terrace loess area foundation is reinforced. The variable-rigidity composite pile composite foundation comprises the multiple vertically-arranged variable-rigidity composite pi