
Concept explainers
Repeat Problem 19-7 using two different depths of untreated aggregate bases of 6 in. and 12 in. Highway contractors in your area can furnish rates for providing and properly laying an asphalt concrete surface and untreated granular base. Assume a structural coefficient of 0.12 for the base course. If these rates are available, determine the cost for constructing the different pavement designs if the highway section is 5 miles long and the lane width is 12 ft. Which design will you select for construction?

The cost for constructing the different pavement designs.
Answer to Problem 13P
Explanation of Solution
Given information:
Following is the given information:
Equivalent single axle load, ESAL =
CBR =
Subgrade resilient modulus =
Sub-base layer coefficient =
Granular base layer coefficient =
Elastic modulus of asphalt concrete =
mi = 1, Percentage of traffic on design lane =
SN = 4, reliability level =
and design serviceability loss =
Calculation:
We have the following formula for the calculation of truck factor:
Where, ESAL i= equivalent accumulated 18,000-lb (80-kN) single-axle load for the axle category i
fd= design lane factor,
G rn= growth factor for a given growth rate r and design period n
AADT i= first-year annual average daily traffic for axle category i
N i= number of axles on each vehicle in category i
F Ei= load equivalency factor for axle category i
Calculate ESAL for passenger car
We have the following formula for the calculation of design serviceability :
Substitute the values in the required equation.
Initial serviceability index,
Terminal serviceability index,
Let's determine the resilient modulus of subgrade:
The resilient modulus of subgrade is 1500 times CBR
The value of resilient modulus is given as follows:
Now for the structural number, SN refer to figure 19.10
The reliability level is 90%. Starting from the point 90% in figure, extend this point to standard deviation 0.45. From standard deviation point, extend this line to line A as given in the figure.
From line A extend this line to
From ESAL extend this line to line B in the figure.
From line B extend this line to
From M rextend this line till it touches the graph. From that point, draw a horizontal line to touch the design serviceability loss, which is 2.
Extend a line vertically and take the structural number SN3reading, which is 2.5 and SN2is 2.3
Then from figure 19.6, for layer coefficient and the resilient modulus for base layer is
From figure 19.10, resilient modulus is
Refer figure 19.7 to determine layer coefficient
Now, considering the thickness aggregate base as 6 inches.
Calculate the minimum thickness.
The layer coefficient,
Substitute the values
Checking the values, we have
As the values match, thus the thickness of subgrade calculated is correct.
Calculate the required minimum thickness of base course D2is 6 inches.
Check whether the calculated thickness agrees with the calculated structural number using equation
Substituting the values, we have
Which is compatible with the structural number calculated already.
And implies that the thickness of the surface calculated is correct.
Now, the required minimum thickness of the sub-base course
By substituting the values, we have
Now, check if the calculated thickness agrees with the calculated structural number of using the following equation:
Substituting the values
Which is compatible with the structural number calculated already.
And implies that the thickness of the surface calculated is correct.
The thickness of surface 4.25 inches.
Now, considering the thickness aggregate base as 12 inches.
Calculate the minimum thickness.
Substitute the values, we have
Thus, the thickness of sub grade is 1.7 in.
Now, the thickness of the base course is given as follows:
Substitute the values.
Which is greater than 2.7, i.e., structural number.
Now, the required minimum thickness of the sub-base course
By substituting the values,
Now, check if the calculated thickness agrees with the calculated structural number of using the following equation
Substituting the values,
Which is compatible with the structural number calculated already.
And implies that the thickness of the surface calculated is correct.
Calculate construction cost for the highway considering thickness of base layer as 6 inches and 12 inches.
The cost is calculated by multiplying the measurement of road with the cost per rate.
Assume cost of surface layer as
For cost of base layer
For cost of sub-base layer
The construction cost of the highway is as follows:
Cost = L X B X t X C
For surface layer :
Substitute the values
5 miles is equal to 26400
For base layer :
Substitute the values
For sub-base layer :
Substitute the values
Now, calculate the total cost as follows:
The construction cost of the highway is as follows:
Cost = L X B X t X C
For surface layer :
Substitute the values
5 miles is equal to 26400
For base layer :
Substitute the values
For sub-base layer :
Substitute the values
Now, calculate the total cost as follows:
Conclusion:
Therefore, out of two cases the construction cost is
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