Repeat Problem 20-19 for a pavement containing doweled joints, 6 inch untreated subbase, and concrete shoulders, using the PCA design method.
What will be an ideal response?
First, determine the estimated ESALs:
2-axle (12,000 lb) single unit trucks:
ESAL = 2(0.4)(28.28)(24,000)(365)(0.40)
ESAL = 79.27 × 106
3-axle (16,000 lb) single unit trucks
ESAL = 3(0.1)(28.28)(24,000)(365)(0.40)
ESAL = 29.73 × 106
Subgrade k = 130 lb/in3
For 6 inch untreated subbase, determine effective k from Table 20.22:
k = 140 + [(230 – 140) / 100] × 30 = 167 lb/in3
Assume a slab 6 inches thick with doweled joints and concrete shoulders.
From Table 20.24, obtain equivalent stress values and then interpolate for
effective k,
Equivalent stress = 304 – ((304 – 289) × (17 / 50)) = 298.9
Stress Ratio = 298.9 / 650 = 0.460
From Table 20.27, determine the erosion factor of 2.72
12,000(1.2) = 14,400
16,000(1.2) = 19,200
Calculate the allowable repetitions (ESALs):
The 6 inch slab is inadequate since the allowable ESALs are less than the
expected ESALs.
Assume a slab 7 inches thick with doweled joints and concrete shoulders.
From Table 20.24, Equivalent stress = 248 – ((248 – 236) × (17 / 50))
= 243.9
Stress Ratio = 243.92 / 650 = 0.38
From Table 20.27, determine the erosion factor of 2.54
12,000(1.2) = 14,400
16,000(1.2) = 19,200
Calculate the allowable repetitions:
Damage percent = 29.73 × 106 / 100 × 106 = 29.73%
The 7 inch slab is adequate, check a 6.5 inch slab.
Assume a slab 6.5 inches thick with doweled joints and concrete shoulders.
From Table 20.24, equivalent stress = 274 – ((274 – 260) × (17 / 50))
= 269.24
Stress Ratio = 269.24 / 650 = 0.41
From Table 20.27, determine the erosion factor of 2.62
12,000(1.2) = 14,400
16,000(1.2) = 19,200
Calculate the allowable repetitions:
The 6.5 inch slab is inadequate, use a 7 inch slab depth.
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