In engineering, roads are structurally divided into subgrade and pavement.

Pavement includes surface layer, base layer and cushion layer, which may not be available. The base layer is a common water-stable layer, and the surface layer is the driving layer. I won't go into details here, each layer is a big article. In addition, subgrade and subgrade are often called soil foundation. Generally speaking, you have cleaned the topsoil, dug a ditch and prepared to lay concrete or asphalt pavement on it. The part of this trench starting from the low soil is called subgrade, and the part near the low soil of the trench is also called subgrade, which is a part of subgrade.

General definition: 0 ~ 80 cm below the bottom of pavement layer is the road bed.

Extended data:

Subgrade design standard

1. Subgrade is the foundation of pavement and bears the load from pavement. Within 500mm below the top surface of the road bed, the soil that meets the requirements of the road bed shall be filled and compacted in layers to achieve uniformity and compactness.

In order to reduce the project cost, the local materials should be selected for the subgrade filler in combination with the material situation at the project site.

2. According to the Technical Specification for Highway Subgrade Construction, the maximum particle size of the subgrade filler of the first-class highway should be less than 100mm, and the minimum CBR (California Bearing Ratio) of the filler should be 8%.

3. The reinforcement of individual subgrade should be carried out according to the actual situation of subgrade, soil quality, precipitation, groundwater type and buried depth, and the source of reinforcement materials. After comparison, reinforcement measures such as in-situ rolling, changing or improving soil, strengthening underground drainage and setting geosynthetics can be adopted. ?

References:

Baidu encyclopedia: road bed