# Pavement Design Factors - IES Previous Year Questions

1.â€ƒThe number of load cycles (N_{f}) to cause the failure of a pavement is proportional to (P is the respective applied load) _____ .

**[IES 1997]**

- P
^{-4} - P
^{2} - P
^{-1} - P
^{4}

**Answer:**Option C

**Explanation:**

If pavement structure fails with N

_{1}number of repetitions of P

_{1}load and similarly if pavement structure fails with N

_{2}number of repetitions of P

_{2}load, then P

_{1}N

_{1}and P

_{2}N

_{2}are said to be equivalent.

P

_{1}N

_{1}= P

_{2}N

_{2}

⇒ PN

_{f}= Constant

⇒ N

_{f}=

Constant / P

⇒ N

_{f}∝

1 / P

2. â€ƒWhich of the following factors have to be considered for the design of the flexible pavement for a highway ?

- Design wheel load
- Strength of pavement component material
- Expansion joints
- Climatic factors

Select the correct answer using the codes given below:

**[IES 2005]**

- 2, 3 and 4
- 1, 3 and 4
- 1, 2 and 4
- 1, 2 and 3

**Answer:**Option C

**Explanation:**

The design of flexible pavement depends on

- Design wheel load
- Subgrade soil
- Climatic factors
- Pavement component materials
- Environmental factors

3. â€ƒWhat is the deflection at the surface of a flexible pavement due to a wheel load of 40 kN and a tyre pressure of 0.5 MPa ? The value of E for pavement and subgrade is 20 MPa.

**[IES 2014]**

- 11 mm
- 9 mm
- 6 mm
- 15 mm

**Answer:**Option C

**Explanation:**

The displacement at the surface of flexible pavement as per Burmister method is given by,

∆ =

1.5 pa / E

x F_{s}_{2}

where,

p - contact pressure = 0.5 MPa

a - radius of contact area

E

_{s}- Youngâ€™s modulus of subgrade = 20 MPa

F

_{2}- factor depending on

Modulus of elasticity of subgrade / Modulus of elasticity of pavement

and Depth / Radius

. Assume F_{2}= 1

Now, contact area =

Wheel load / Tyre pressure

= 40 x 10

= 80 x 10^{3}/ 0.5^{3}N/mm

^{2}

⇒ π x a

^{2}= 80 x 10

^{3}

⇒ a = 159.58 mm

Thus, ∆ =

1.5 pa / E

x F_{s}_{2}=

1.5 x 0.5 x 159.58 / 20

x 1 ⇒ ∆ = 5.98 mm ≈ 6 mm

4. â€ƒWhich one of the following statements is correct ?

**[IES 2020]**

- The ratio of load on the wheel to contact pressure is called as rigidity factor.
- The value of rigidity factor is more than three for an average tyre pressure of 7 kg/cm
^{2}. - Rigidity factor does not depend upon the degree of tension developed in walls of tyres.
- The ratio of load on the wheel to contact area or area of imprint is called as contact pressure.

**Answer:**Option D

**Explanation:**

- The ratio of contact pressure to tyre pressure is called the rigidity factor.
- The value of rigidity factor is 1.0 for an average tyre pressure of 7 kg/cm
^{2}. - The rigidity factor depends upon the tension developed in the walls of the tyres.

5. â€ƒThe thickness design of pavement mainly depends on _____ .

**[IES 2022]**

- The climatic factors
- The design wheel load
- The subgrade soil
- The pavement materials

**Answer:**Option B

**Explanation:**

Design wheel load is the primary factor to be considered while designing the thickness of a pavement. Higher the wheel load thicker is the pavement to be provided. The design of flexible pavement depends on

- Design wheel load
- Subgrade soil
- Climatic factors
- Pavement component materials
- Environmental factors