Which layer lies directly beneath the Surface Course on a runway?

Which layer lies directly beneath the Surface Course on a runway?

• A. Base Course
• B. Sub-base Course
• C. Surface Course
• D. Overlay

Answer: (A)

In runway pavement structure, the Surface Course is the top wearing layer exposed to traffic and weather, while the layer directly beneath it provides the main structural support. That immediate lower layer is the Base Course, which distributes loads from the surface to the layers below and helps prevent deformation, while also contributing to drainage and frost resistance. Beneath the Base Course sits the Sub-base Course, then the Subgrade (the natural soil). An overlay, if added, would go on top of the Surface Course, not beneath it. So the layer directly beneath the Surface Course is the Base Course.

In runway pavement structure, the Surface Course is the top wearing layer exposed to traffic and weather, while the layer directly beneath it provides the main structural support. That immediate lower layer is the Base Course, which distributes loads from the surface to the layers below and helps prevent deformation, while also contributing to drainage and frost resistance. Beneath the Base Course sits the Sub-base Course, then the Subgrade (the natural soil). An overlay, if added, would go on top of the Surface Course, not beneath it. So the layer directly beneath the Surface Course is the Base Course.