What are the functions of different pavement layers?

Pavement layers from bottom up: Subgrade - natural ground supporting the pavement, compacted and graded. Subbase - granular layer spreading loads and preventing subgrade pumping. Base - main structural layer distributing wheel loads. Surface/wearing course - provides smooth riding surface, skid resistance, and waterproofing. Each upper layer must be stronger than the layer below to effectively spread loads. Total thickness depends on traffic loading and subgrade strength.