Consider the following statements regarding the function of base course and sub-base course in pavement layers: i. Prevent mud-pumping in rigid pavement ii. Protect sub-grade of rigid pavement from frost action iii. Provide tensile strength to the flexible pavement iv. Distribute the load in flexible pavement v. Prevent warping stresses in rigid pavement. Which of the above statements are correct?
- AOnly i, ii and v
- BOnly ii, iii and v
- COnly i, ii and ivCorrect
- DBoth ii and iv
Solution
Concept
Base and sub-base distribute load (flexible), prevent mud pumping, and protect the subgrade from frost (rigid).
Step-by-step solution
1. Statement i: In rigid pavement, the base or sub-base stops fine soil from being pumped out at joints. It is correct. 2. Statement ii: A granular base or sub-base protects the subgrade from frost action. It is correct. 3. Statement iii: Granular layers have almost no tensile strength. It is wrong. 4. Statement iv: In flexible pavement, base and sub-base spread the wheel load over a wider area. It is correct. 5. Statement v: Warping stresses come from temperature difference in the slab. A sub-base cannot prevent them. It is wrong. 6. The correct statements are i, ii and iv. Answer: C.
Explanation
In flexible pavement, base and sub-base mainly spread the wheel load to the subgrade. In rigid pavement, they prevent mud pumping and protect the subgrade from frost. They do not give tensile strength and do not stop warping stresses.
Why the other options are wrong
A: It includes v, but warping cannot be prevented by the base. B: It includes iii and v, which are wrong. D: It misses statement i, mud-pumping prevention, which is a main function.
Shortcut
Base and sub-base give load spread, drainage and frost protection. They give no tension and no control of warping.
Common mistake
Students think the base can reduce warping stresses. Warping depends on the temperature gradient in the slab.
Correct answer: C) Only i, ii and iv