What material is the subgrade of expressway made of?

Pavement is the general name of each structural layer supported on subgrade. Pavement structure layer is generally composed of surface layer, base layer and cushion layer. \x0d\ Pavement not only bears wheel load, but also is affected by natural environment factors. Due to the influence of traffic load and atmospheric factors on the pavement, it generally weakens with depth, so the pavement is usually a multi-layer structure, with good quality materials laid on the upper layer with greater stress and poor quality materials laid on the lower layer with less stress, thus forming a pavement structure with different specifications and required materials on the subgrade. \x0d\\x0d\ Asphalt concrete and cement concrete are the main materials for building high-grade road pavement. \x0d\\x0d\ The materials used to build the base mainly include: cement, lime, asphalt and other stabilized soil or stabilized granular materials (such as crushed stone and gravel), industrial waste residue stabilized soil or stabilized granular materials, various crushed stone mixtures or natural gravel. \ x0d \ x0d \ cushion strength is not necessarily high, but it is better in heat insulation and waterproof. Generally, coarse sand, gravel, gravel, cinder, slag and other loose granular materials are selected according to the principle of local materials, or dense cushion stabilized by cement and lime cinder is adopted.