Question

Arrange the following components of a typical flexible pavement from bottom to top in correct sequence:
A. Prepared soil subgrade
B. Granular subbase cum drainage layer
C. Granular base course
D. Surface course
Choose the correct answer from the options given below :

• A. A, C, B, D
• B. A, B, C, D
• C. B, A, C, D
• D. C, D, A, B

Hint:

Mnemonic: "S-SB-B-S" (Subgrade, Subbase, Base, Surface). Remember that materials get "stronger and more expensive" as you move from the bottom to the top of the pavement!

Answer 1

The Correct Option is B

Concept: A flexible pavement is a layered structure designed to distribute traffic loads to the underlying soil. The quality and strength of the materials increase from the bottom layer to the top layer.

Step 1: Identify the foundation layer.
The bottom-most layer is the Prepared soil subgrade (A), which is the natural or compacted soil that acts as the ultimate foundation for the entire pavement structure.

Step 2: Identify the intermediate drainage and structural layers.
Directly above the subgrade is the Granular subbase (B), which provides structural support and acts as a drainage layer to prevent water from reaching the subgrade. Above the subbase is the Granular base course (C), which provides the main structural capacity to distribute the high stresses from the surface.

Step 3: Identify the wearing layer.
The top-most layer is the Surface course (D) (or Wearing course), which directly contacts vehicle tires, provides a smooth riding surface, and protects the lower layers from surface water.