# Foundation Engineering Questions and Answers – Design of Rigid Pavements

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This set of Foundation Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Design of Rigid Pavements”.
1. A base under rigid pavements is used for the ___________
a) preservation of pumping of fine grained soils
b) pumping of fine grained soils
c) surface coating
d) finishing

Explanation: The base course of the rigid pavement consists of dry mix of cement and granular materials or aggregates which can prevent the seepage of fine grained particles to the rigid pavement surface.

2. When load is applied on rigid pavement, it deforms in a _______
a) bottle shape
b) saucer shape
c) rectangular shape
d) square shape

Explanation: When load is applied on rigid pavement, it deforms in a saucer shape. This is due to the fact that the rigid pavements are designed on the basis of the design of slabs and their deflections are in the saucer shape.

3. The radius of relative stiffness is given by the characteristic equation of _______
a) $$l=\{\frac{eh^3}{12(1-μ^2 ) k_s}\}^\frac{1}{4}$$
b) $$l=\{\frac{eh^3}{12(1-μ^4 ) k_s}\}^\frac{1}{4}$$
c) $$l=\{\frac{eh^3}{12(1-μ^2 ) k_s}\}^\frac{1}{2}$$
d) $$l=\{\frac{eh^3}{12(1-μ^2 ) k_s}\}^\frac{1}{3}$$

Explanation: The radius of relative stiffness is given by the characteristic equation of,
$$l=\{\frac{eh^3}{12(1-μ^2 ) k_s}\}^\frac{1}{4},$$
E=elasticity modulus
h=thickness of pavement
μ=Poisson’s ratio

3. If P is the vertical relation and ρ is the vertical deflection, then the modulus of sub-grade reaction is _______
a) $$k_s=\frac{P}{ρ}$$
b) $$k_s=\frac{1}{P}$$
c) $$k_s=\frac{ρ}{P}$$
d) $$k_s=\frac{P}{2ρ}$$

Explanation: The modulus of sub-grade reaction is defined as the intensity of pressure on the horizontal surface of a soil mass required to cause a unit settlement of surface.
∴ $$k_s=\frac{P}{ρ}.$$
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5. A base course enables the construction to proceed during wet weather on clays and silts.
a) True
b) False

Explanation: The base course forms a working surface on clays and silts. Thus, the base course enables the construction to proceed during wet weather on clays and silts.

6. The stresses in rigid pavement are due to ________
a) restrained temperature only
c) frost action only
d) restrained temperature, external loads and frost action

Explanation: The factors affecting stresses in rigid pavements are broadly placed in four categories:

• Stresses due to restrained temperature and moisture deformation
• Stresses due to external loads
• Stresses due to volume changes of supporting material and frost action
• Stresses due to continuity of sub-grade support.

6. The temperature in general at the bottom of the slab is __________
a) constant
b) variant
c) constant during the days only
d) constant during the nights only

Explanation: The surface of the slab is subjected to a wide range of temperatures during the daily cycle. As far as the bottom surface is considered, the temperature in general is relatively more constant.

7. In a day, the top surface of rigid pavement ______ than the bottom of slab.
a) expands
b) contracts
c) remains stable
d) shows no changes

Explanation: In a day, as the temperature in the top of rigid pavement is hot or at least more than that of the bottom, the the top surface of rigid pavement expands more than the bottom of slab.

8. If there is no friction between the slab and the sub-grade, then there are ______ in slab.
a) no stresses
b) small number of stresses
c) large number of stresses

Explanation: The stresses are set up in the slab due to uniform temperature changes. If this is absent and the slab is free to move without resistance, then there is no friction between the slab and sub-grade. Thus, if there is no friction between the slab and the sub-grade, then there are no stresses in slab.

9. During expansion the under-side of the slab is subjected to _________
a) tensile stress
b) shearing stress
c) compressive stress
d) bulk stress

Explanation: During expansion the under-side of the slab is subjected to compression. This can be visualised by the hogging action of the beam where the under-side is in compression.

10. During contraction, _________ are induced in the under-side of the slab.
a) tensile stress
b) shearing stress
c) compressive stress
d) bulk stress

Explanation: During contraction, the tensile stresses are induced in the under-side of the slab. This can be visualised by the sagging action of the beam where the under-side is in tension. This is also due to the tensile stresses induced due to the sub-grade friction.

11. The critical stress condition in slab is when _________
a) temperature and load stresses are multiplicative
c) temperature and load stresses oppose each other
d) critical stress condition does not occur in slab

Explanation: The critical stress condition in the slab is the one in which the stresses due to temperature and stresses due to load are additive. This takes place when the slab corners are wrapped down.

12. The critical stress condition in slab occurs when __________
a) corners remain unwrapped
b) corners are wrapped upward
c) corners are wrapped downward
d) corners are wrapped laterally

Explanation: The critical stress condition in slab is when temperature and load stresses are additive. This happens when the road is hot in day and cold in night. When the corners are wrapped downward, the critical stress condition in slab occurs.

13. The critical stress condition in slab occurs when __________
a) load is applied at exterior of the slab
b) load is applied at exterior and interior of the slab
d) load is applied at interior of the slab

Explanation: When the corners are wrapped downward, the critical stress condition in slab occurs and this situation occurs when the load is applied at interior of the slab.

14. During the clear, cool night followed by a hot sunny day, the edges and corners of slab will ____________
a) wrap downward
b) wrap upward
c) wrap upwards and downwards
d) wrap laterally

Explanation: During the clear, cool night followed by a hot sunny day, the edges and corners of slab will wrap upward. When this occurs, the corners may be partially supported or even unsupported in some cases.

15. The base course in rigid pavement provides drainage.
a) True
b) False

Explanation: The base course in rigid pavement provides drainage. This is true as the base course is made of aggregates that have voids between their solid particles which allow the flow of water through it, thus making it permeable.

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