Pavement Design Multiple Choice Questions on “Highway Pavements Design – CBR Method”.

1. ______ proposed the original curves for the design of flexible pavements using CBR method.

a) H. M. Westergaard

b) F. M. Hveem

c) O. J. Porter

d) D. J. Steel

Answer: c

Clarification: The original curves for developing the design curves for the flexible pavement using CBR method was first proposed by O. J. Porter. H. M. Westergaard put forward the analysis for rigid pavements, F. M. Hveem developed a method for the mix design of bituminous mixes and D. J. Steel proposed the use of soil classification for design.

2. The equation (t=sqrt P (frac{1⋅75}{CBR}-frac{1}{pπ})^{1⁄2}) is valid only when the value of CBR is ______

a) More than 15%

b) Less than 15%

c) More than 12%

d) Less than 12%

Answer: d

Clarification: The equation (t=sqrt P (frac{1⋅75}{CBR}-frac{1}{pπ})^{1⁄2}) was proposed by US Corps of Engineers to determine the thickness of pavement based on the CBR value. This equation is only valid for a CBR value of less than 12%. They had developed it for values of CBR ranging from 10-12%.

3. How are the traffic volume considerations in the design chart developed by IRC denoted as?

a) Alphabets

b) Alphanumeric

c) Numeric

d) Percentages

Answer: a

Clarification: The traffic volume in the design charts by IRC is denoted using alphabets ranging from A to G. A has the least traffic volume and it increases with G having the highest.

4. Which of the below is not a classification of traffic condition that is used in the CBR design chart?

a) Normal traffic 2500 kg

b) Light traffic 3175 kg

c) Medium traffic 4082 kg

d) Heavy traffic 5433 kg

Answer: a

Clarification: The design charts developed for CBR method by the California State of Highways makes use of three traffic conditions. They are light traffic, medium traffic and heavy traffic. There is no condition of normal traffic used in the design charts.

5. Calculate the total thickness of the pavement if the CBR value of the soil is 7%, the wheel load is 4100 kg and the tyre pressure is 7 kg/cm^{2}.

a) 2896 mm

b) 28.96 cm

c) 2896 cm

d) 28.96 mm

Answer: b

Clarification: The CBR value can be found out using the equation (t=sqrt P (frac{1⋅75}{CBR}-frac{1}{pπ})^{1⁄2}) according to the conditions given in the question.

CBR = 7%, P = 4100 kg and p = 7 kg/cm^{2}

(t=sqrt{4100}(frac{1⋅75}{7}-frac{1}{7π})^{1⁄2}) =28.96 cm

6. Determine the thickness of the pavement if the pavement is subjected to medium traffic and the CBR value is obtained as 7%.

a) 33 cm

b) 31 cm

c) 35 cm

d) 34 cm

Answer: b

Clarification: The data given in the question is traffic condition and CBR value. The California State of Highways design chart is to be used. A sample of the same graph is given below. In the graph, curve A represents 3175 kg wheel load or light traffic, curve B represents 4082 kg wheel load or medium traffic and curve C represents 5443 kg wheel load or heavy traffic. The value corresponding to medium traffic and 7% CBR can be obtained from the chart as 31 cm.

7. IRC 37-1984 redesigned the CBR charts based on ______

a) Wheel loads

b) Cumulative load

c) Design traffic

d) Cumulative standard axle

Answer: d

Clarification: IRC 37-1970 used the design chart similar to that developed by the California State Highways, using the CBR value and the traffic volume. Later the charts were redesigned based on the cumulative standard axle (csa) and CBR value.

8. The CBR value of the soil is found out to be 6% and the traffic is 350 commercial vehicles per day. Find the pavement thickness using design charts provided by IRC.

a) 37 cm

b) 35 cm

c) 33 cm

d) 30 cm

Answer: b

Clarification: A sample of the design chart for computing the thickness of pavement using CBR method by IRC is shown below. The curve D is to be considered as the commercial vehicles per day is 350 which lies between 150 and 450. The thickness corresponding to 6% CBR and curve D is obtained as 35 cm.