Surfaces persist in an AutoCAD drawing as objects with the names AECC_TIN_SURFACE (TIN surface) or AECC_GRID_SURFACE (grid surface).
All AutoCAD Civil 3D objects are aware of each other and react to changes. For example, a change in a surface results in multiple automatic updates in alignments, parcels, or other objects that reference that surface.
For overview information about AutoCAD Civil 3D objects, see Understanding Civil 3D Objects.