Subgrade Design and Construction （路基设计与施工）.pdfVIP

6E-1 Design Manual Chapter 6 - Geotechnical 6E - Subgrade Design and Construction Subgrade Design and Construction A. General Information The subgrade is that portion of the pavement system that is the layer of natural soil upon which the pavement or subbase is built. Subgrade soil provides support to the remainder of the pavement system. The quality of the subgrade will greatly influence the pavement design and the actual useful life of the pavement that is constructed. The importance of a good quality subgrade to the long term life of the pavement cannot be understated. As the pavement reaches design life, the subgrade will not have to be reconstructed in order to support the rehabilitated subgrade or the reconstructed pavement. In urban areas, subgrade basic engineering properties are required for design. This section summarizes the design and construction elements for subgrades. B. Site Preparation Site preparation is the first major activity in constructing pavements. This activity includes removing or stripping off the upper soil layer(s) from the natural ground. All organic materials, topsoil, and stones greater than 3 inches in size should be removed. Removal of surface soils containing organic matter is important not only for settlement, but also because these soils are often moisture-sensitive, they lose significant strength when wet and are easily disturbed under construction activities. Most construction projects will also require excavation or removal of in-situ soil to reach a design elevation or grade line. C. Design Considerations Subgrade soil is part of the pavement supp