1. Subgrade: Subgrade is the foundation of pavement and must be solid and firm. Due to the change of terrain, it is generally divided into embankment and road thorn.

2. Subgrade: Subgrade refers to the part of subgrade within 80cm below the bottom of the pavement, which bears the load from the pavement. The main function of subgrade is to provide conditions for the laying of tracks or roads and the operation of trains or vehicles, to bear the static and dynamic loads of tracks and locomotives or roads, as well as traffic loads, and at the same time to transmit and disperse the loads to the depths of foundation.