Using finite difference method

the fluid-mechanical interaction model is established with FLAC for powdery soil subgrade of highway in alluvial plain of the Yellow River. Considering the process of discharge of the pore fluid and layered constructing in the actual roadbed construction

the process of the powdery subgrade deformation is analysed and compared with the result of fieldwork. The results show that

for ordinary section of a highway

the pavement structure can be directly constructed after the roadbed completed if the height of the roadbed ≤10 m; and the allowable subgrade deformation after 6 months of pavement structure completed can not be satisfied if the height of the roadbed ≥12 m. For the head of bridge

the two limits are ≤6 m and ≥8 m of the height of roadbed respectively. For the culvert and channels

they are ≤8 m and ≥10 m respectively.