Using the information given in Problem 19-6, design a suitable pavement consisting of an asphalt mixture surface with an elastic modulus of 250,000 lb/in2, a granular base layer with a structural coefficient of 0.14 on a subgrade having a CBR of 10. Assume all mi values = 1, and the percent of traffic on the design lane is 45%. Use a reliability level of 85%, a standard deviation of 0.45, and a design serviceability loss of 2.0.

Question

What will be an ideal response?

Answer 1

From Problem 19-6, ESAL = 4.20 × 105
Using Equation 19.3, Mr = 1,500(CBR) = 15,000 lb/in2
Using the nomograph in Figure 19.10,
Step 1: Connect Reliability of 85% to standard deviation of 0.45 and
extend to first turning line to create “A”
Step 2: Connect “A” to ESAL of 4.20 × 105 and extend to second turning
line to create “B”
Step 3: Connect “B” to Mr of 15 × 103 and extend to design serviceability
loss chart to create “C”
Step 4: Connect “C” to ?PSI of 2.0
Step 5: Draw vertical line to read SN of 2.4
Determine structural coefficients for each layer
From Figure 19.7, with EAC = 250,000 lb/in2
a1= 0.33
Since this pavement is being designed with two layers, equation 19.6 can be
modified for use in this problem as:
SN = a1D1 + a2D2m2
2.4 = (0.33)D1 + (0.14)D2(1)
From Table 19.11, for 4.00 × 105 ESALs, a recommended minimum
thickness of asphalt concrete is 2.5 inches and 4 inches for aggregate base.
The structural number provided using these minimums can then be found:
SN = (0.33)(2.5) + (0.14)(4)(1) = 1.385
Since this SN is below that required, layer thicknesses will need to be
increased in order to provide sufficient support. If the asphalt concrete
thickness is held at 2.5 inches, the required thickness of the base course
can then be found:
2.4 = (0.33)(2.5) + (0.14)D2(1)
D2 = 11.25 inches ? round up to 12 inches.