An existing two-lane rural highway is to be replaced by a four-lane divided highway on a new alignment. Construction of the new highway will commence two years from now and is expected to take three years to complete. The design life of the pavement is 20 years. The present ESAL is 150000. Design a flexible pavement consisting of an asphalt concrete surface and lime-treated base using the California (Hveem) method. The base has an R value of 80. The results of a stabilometer test on the subgrade soil are as follows.
What will be an ideal response?
Total ESAL = 150000 × (47.73 – 5.53) = 6.33 × 106
Calculate traffic index using Equation 19.8,
TI = 9.0(6.33)0.119 = 11.21
Next, calculate thickness above base using Equation 19.11:
GE = 0.0032(TI)(100 – R)
GE = 0.0032(11.21)(100 – 80)
GE = 0.717 ft.
From Table 19.12, Gf for asphalt concrete with TI of 11.21 = 1.71
Actual depth of AC = 0.717/1.71 = 0.419 ft = 5 in.
Next, calculate base thickness
To determine GE at 300 lb/in2, Plot GE vs. Exudation pressure
At 300 lb/in2, GE = 2.5
From Table 19.12, for lime-treated base, Gf = 1.2
GE of base layer = 2.5 – (5/12)(1.717) = 1.785
Base thickness = 1.785 / 1.2 = 1.4896 ft. = 17.85 in. Use 18 in.
Check design:
Plot GE vs. Moisture content to determine moisture content at 300 lb/in2
From plot above, right, Moisture content = 23.5%
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