Abstract: Using test, the engineering characteristics of soil in flooded area by the Yellow River are studied. The constitution characteristics, grain microstructure and physico-mechanical characteristics of the soil are analyzed with x-ray and electronic probe etc. Its compaction mechanics and property is studied too. The soil presents in layer structure, and is mainly made up of silicon and aluminum in chemical constitution. The content of silt is more than 80 %, and its gradation is worse. The grain has high psephicity and severe surface flaking because of the long transport function of water. Consequently it’s difficult to form availably contact between grains, and expressing bad compaction characteristics. When the compaction reaches 90%, the soil has bigger compressibility, because the pore air volume is rather larger. While the compaction rising from 95 % to 98 %, the density and bearing capacity increase obviously. The holding power of low-filling roadbed is inadequate on the condition of overloading seriously, owing to the severe capillarity and high humidity inside the 1.3 m scope above the underground water level.

Key words: Yellow River, silt, subgrade, compaction