Compaction thickness refers to the thickness of compacted layer of soil or other building materials during road construction.

Earthwork compaction is a construction operation that uses human or mechanical force to force soil particles to compact each other and increase soil compactness. Compaction can expel some air from the soil, increase the compactness and shear strength of the soil, reduce the compressibility of the soil, improve its impermeability and increase the uniformity of geotechnical buildings. Compaction methods generally include rolling method, tamping method, vibration compaction method and compaction with earth-moving tools. For muddy earthwork, there are surcharge preloading method and vacuum preloading method.

Subgrade: it is a belt-shaped structure built as the foundation of pavement according to the location of the line and certain technical requirements, and it is the foundation of railways and highways. Subgrade is a linear structure made of earth or stone. Build subgrade under good geological, hydrological and climatic conditions. As far as materials are concerned, subgrade can be divided into three types: soil subgrade, stone subgrade and earth-rock subgrade.