# Pavement Design Questions and Answers – GI and Triaxial Method – 1

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This set of Pavement Design Multiple Choice Questions & Answers (MCQs) focuses on “GI and Triaxial Method – 1”.

1. What is the range of values of group index for a good soil?
a) 0 to 1
b) 2 to 4
c) 5 to 9
d) 10 to 20

Explanation: The range of group index values for a good soil is 0 to 1. For a fair soil, the value is in between 2 and 4. A poor soil has group index values ranging from 5 to 9 and a very poor soil has values from 10 to 20.

2. Who proposed the triaxial method of design for flexible pavements?
a) L. A Barber and E. S Palmer
b) F. M Hveem and R. M Carmany
c) L. A Palmer and E. S Barber
d) F. M Carmany and R. M Hveem

Explanation: The triaxial method of designing the flexible pavement was developed by L. A Palmer and E. S Barber in the year 1910. F. M Hveem and R. M Carmany developed the California Resistance Value method for the design of flexible pavements.

3. What test can be carried out to obtain the group index?
a) Specific gravity
b) Density
c) Sieve analysis
d) Particle index

Explanation: Th group index is based on the soil particle sizes. The equation for group index has terms that are related to the percentage of the size of particles passing particular sieves. So, sieve analysis is the test that will give the values to be substituted in the equation.

4. The triaxial compression test is used to determine the ______ of various materials.
a) Shear strength
b) Modulus of elasticity
c) Moisture content
d) Compressive stress

Explanation: The triaxial method is based on the triaxial compression test results. It is used to find the modulus of elasticity of various materials. It is obtained from the stress-strain curve.

5. Using the design charts for the group index, only the complete pavement thickness can be read.
a) True
b) False

Explanation: The design charts used for the design of pavement thickness using the group index method gives two separate thickness values. One is the combined thickness for surface, base, and sub-base; and the other one is for surface and base.

6. What data is required for computing thickness of pavement by group index method?
a) Traffic volume and group index
b) Traffic rate and group index
c) Traffic intensity and group index
d) Traffic index and group index

Explanation: There are design charts available to calculate the thickness of pavement using the group index method. The data required to read values from the chart are traffic volume in terms of commercial vehicles per day and the value of the group index of the soil.

7. A soil sample is subjected to sieve analysis and the following data is obtained:
Percentage passing 0.074 mm sieve = 64%
Liquid limit = 53%
Plastic limit = 36%
a) 13
b) 11
c) 12
d) 10

Explanation: The equation GI = 0.2a+0.005ac+0.01bd can be used to find the group index.
where “a” represents the portion of material passing 0.074 mm sieve, greater than 35 but not exceeding 75% (represented as a whole number in the range 0-40),
“b” represents the portion of material passing 0.074 mm sieve, greater than 15 but not exceeding 35% (expressed as a whole number in the range 0-40),
“c” represents the liquid limit in excess of 40 but less than 60 (expressed as a whole number in the range 0-20),
“d” represents the plasticity index in excess of 10 but less than 30 (expressed as a whole number in the range 0-20)
The following can be interpreted from the data given in the question.
Plasticity index = liquid limit – plastic limit = 53 – 36 = 17
a=64-35=29
b=64-15=49
c=53-40=13
d=17-10=7
GI =0.2×29+0.005×29×13+0.01×49×7=11.12≈11

8. Traffic coefficient is the factor that has been added to the triaxial equation to obtain the modified triaxial equation.
a) True
b) False

Explanation: Two factors have been added to modify the basic triaxial equation. Traffic coefficient and saturation/rainfall coefficient are the two factors considered. It is multiplied with the basic equation. This is done when the soil is considered as a single layer homogeneous mass.

9. Find the thickness of pavement if the triaxial test is conducted on a sample and the data obtained are:
Wheel load, P = 4100 kg
Radius of contact area, a = 16 cm
Traffic coefficient, X = 1
Rainfall coefficient, Y = 0.9
Deflection, = 0.25 cm
Modulus of elasticity, E = 100 kg/cm2
a) 86.36 cm
b) 68.63 cm
c) 86.63 cm
d) 68.36 cm

Explanation: The equation for the thickness of pavement using the triaxial method can be written as:
$$T=\sqrt{\left(\frac{3PXY}{2πEΔ}\right)^2-a^2}$$
Now after substituting values from the question,
$$T=\sqrt{\left(\frac{3×4100×1×0.9}{2π×100×0.25}\right)^2-16^2}=68.63 cm$$.

10. The group index of the soil is found to be 5 and the traffic condition expected is medium traffic. What would be the combined thickness to be provided on the pavement for bearing the loads to ensure smooth conduct of traffic.
a) 24 cm
b) 38 cm
c) 34 cm
d) 28 cm

Explanation: Since the group index values and the traffic condition is already provided, the thickness can be directly read from the design chart. The chart has been provided by the Highway Research Board, USA. A sample of the graph showing the curve for combined thickness of the surface, base and sub-base course for medium traffic condition is shown below.

The combined thickness of the surface, base and sub-base course for group index of 5 can be obtained as 34 cm from the chart.

11. What term is added to the modified triaxial equation in order to incorporate the elasticity of the pavement?
a) Elasticity factor
b) Stiffness factor
c) Elasticity ratio
d) Stiffness ratio

Explanation: In the modified triaxial equation, in order to incorporate the two-layer system, it is necessary to include the modulus of elasticity of the pavement along with the modulus of elasticity of the subgrade. Stiffness factor is the term that is used for the same.

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