The granular sub bass forms the lowest (bottom) layer of the pavement structure,
and acts as the principal foundation for the subsequent road profile, provides
drainage for the pavement structure, and protects the structure from frost.
A mixture of soil particles ranging in size from coarse to fine. Processing
involve crushing oversized particles and screening where it is necessary to secure
the desired grading. The requirements of a satisfactory soil aggregate surface are:
Stability.