Pavement Design: ESALs & Structural Number

Worked: filling in the subbase

The design calls for SN = 4.2, with m = 1.0. Four inches of asphalt supply 4 × 0.44 = 1.76 and ten inches of base 10 × 0.14 = 1.40, for 3.16. The subbase must make up 1.04: D₃ = 1.04/0.11 = 9.5 in, so specify 10 in, giving SN = 4.26.

The fourth-power rule is why trucks govern: one 24 kip axle does (24/18)⁴ = 3.2 times the damage of the standard axle, and a 12 kip axle only 0.2.