Rigid Pavement Design - IES Previous Year Questions

1. Given that, r = radius of load distribution, E = modulus of elasticity of concrete, K = modulus of subgrade reaction, µ = Poisson’s ratio of concrete, h = thickness of slab, P = wheel load. The combination of parameters required for obtaining the radius of relative stiffness of cement concrete slab is _____ .

[IES 1995]

  1. h, K, µ, r
  2. E, h, K, µ
  3. P, h, K, µ
  4. E, K, µ, r
Answer: Option B
Explanation:
The radius of relative stiffness, l = {
Eh3 / 12 K(1 - μ2)
}¼
Where,
E - Young’s modulus of cement concrete
h - Thickness of cement concrete slab
K - modulus of subgrade reaction
μ - Poisson’s ratio for concrete

2. Effect of impact on the design of rigid pavements is accounted for by _____ .

[IES 1996]

  1. Increasing the thickness as would be calculated with static wheel load. 
  2. Providing a base course.
  3. Adopting a reduced flexural strength of concrete through a factor of safety.
  4. Adopting an increased stress relative to that produced by static wheel load.
Answer: Option A
Explanation:
The load carrying capacity of a rigid pavement is due to its rigidity and its high modulus of elasticity. The impact load will produce stresses higher than the static wheel load. Hence, due to impact loads, thickness of the pavement calculated for the static wheel loads.

3.  Consider the following statements with reference to pavements: 

  1. Flexible pavements are more suitable than rigid pavements in regions where subgrade strength is uneven.
  2. Load carrying capacity of rigid pavements depends more on the properties of concrete than the strength of subgrade.
  3. Compared to flexible pavements, rigid pavements are more affected by temperature variations. 

Which of these statements is/are correct ?

[IES 1996]

  1. 1 and 3
  2. 2 and 3
  3. 3 alone
  4. 1 and 2
Answer: Option B
Explanation:
Flexible pavements are suitable in regions where the subgrade strength is even. If the subgrade strength is uneven, it will result in local deformations in the flexible pavements.

4.  Assertion (A): Load stresses added to warping stresses are considered while determining the thickness of pavement.

Reason (R): Joints and sealing devices are used to relieve and/or take care of warping stresses, and the design for thickness is accordingly based upon load alone.

[IES 1997]

  1. Both A and R are true and R is the correct explanation of A.
  2. Both A and R are true but R is not a correct explanation of A.
  3. A is true but R is false. 
  4. A is false but R is true.
Answer: Option A
Explanation:
  • As per IRC 58:1988 Clause 4.1, stress due to the traffic loads and temperature stress are considered for determining the thickness of the rigid pavement. Warping stress and frictional stress constitute temperature stress.
  • If joints and sealing devices are used, critical stress combination is determined by adding frictional stress during summer and subtracting frictional stress during winter.

5.  The general requirement in constructing a reinforced concrete road is to place a single layer of reinforcement _____ .

[IES 1998]

  1. Near the top of the slab.
  2. At the middle.
  3. Equally distributed at the top and bottom.
  4. Near the bottom of the slab.
Answer: Option B
Explanation:
As per IRC 101:1988 Clause 5, the steel reinforcements must be placed over suitable chairs at mid depth of the slab.
6.  If the load, warping and frictional stresses in a cement concrete slab are 210 N/mm2, 290 N/mm2 and 10 N/mm2 respectively, the critical combination of stresses during summer mid-day is ____ .

[IES 1999]

  1. 390 N/mm2
  2. 490 N/mm2
  3. 590 N/mm2
  4. 290 N/mm2
Answer: Option B
Explanation:
The critical combination of stress during summer mid-day = Load stress + Warping stress - Frictional stress = 210 + 290 - 10 = 490 N/mm2

7.  In cement concrete pavements, tie bars are installed in _____ .

[IES 1999]

  1. Contraction joints
  2. Warping joints
  3. Longitudinal joints
  4. Expansion joints
Answer: Option C
Explanation:
Tie bars are provided along the longitudinal joints in cement concrete pavements.
8.  If the modulus of subgrade reaction of a soil is 10 kg/m3 when tested with a 30 cm diameter plate, the corrected modulus of subgrade reaction for the standard diameter plate will be _____ .

[IES 2000]

  1. 15
  2. 20
  3. 25
  4. 4
Answer: Option D
Explanation:
The modulus of subgrade reaction is calculated using the standard plate of diameter 75 cm.
As per Burmister method,
Δ =
1.18 pa / Es
x F2
⇒
p a / Δ
=
Es / 1.18 F2
= constant
⇒ K a = constant {Since, p/Δ = K}
⇒ K1 a1 = K2 a2
⇒ K1 =
10 x 30 / 75

⇒ K1 = 4 kg/m3

9.  Assertion (A): The critical combination of stresses on a cement concrete pavement during summer is given by: load stress – warping stress + frictional stress.

Reason (R): The critical combination of stresses in a cement concrete pavement during winter is given by: load stress + warping stress + frictional stress.

[IES 2000]

  1. Both A and R are true and R is the correct explanation of A.
  2. Both A and R are true but R is not a correct explanation of A.
  3. A is true but R is false. 
  4. A is false but R is true.
Answer: Option D
Explanation:
  • The critical combination of stress during summer mid-day = Load stress + Warping stress - Frictional stress, at edge region.
  • The critical combination of stress during summer and winter mid-night = Load stress + Warping stress, at corner regions.
  • The critical combination of stress during winter mid-day = Load stress + Warping stress + Frictional stress, at edge region.

10.  Modulus of subgrade reaction using a 30 cm diameter plate is obtained as 200 N/cm3. The value of the same (in N/cm3) using the standard plate will be _____ .

[IES 2001]

  1. 200
  2. 85
  3. 80
  4. 500
Answer: Option C
Explanation:
The modulus of subgrade reaction is calculated using the standard plate of diameter 75 cm.
As per Burmister method,
Δ =
1.18 pa / Es
x F2
⇒
p a / Δ
=
Es / 1.18 F2
= constant
⇒ K a = constant {Since, p/Δ = K}
⇒ K1 a1 = K2 a2
⇒ K1 =
200 x 30 / 75

⇒ K1 = 80 N/cm3
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