Flexible Pavement SN and ESALs

S N = a_{1} D_{1} + a_{2} D_{2} m_{2} + a_{3} D_{3} m_{3}, lo g_{10} W_{18} = f (S N, p_{t}, M_{R}, Δ P S I)

AASHTO ’93: layer coefficients a_i × thicknesses D_i (inches) plus drainage m_i. Design ESALs W18 from truck factors. Rigid pavement uses k (modulus of subgrade reaction) instead of SN.

$a_{i}$: Layer coefficient
$D_{i}$: Thickness (in)
$W 18$: 18-kip ESAL over the life

Step-by-step solved example

a1=0.44, D1=5 in, a2=0.14, D2=8, m2=1.0. SN of these two layers?

Layer cake: a_i D_i building SN of a flexible pavement.

1. Surface
0.44×5=2.20.
2. Base
0.14×8×1=1.12, SN=3.32.

Answer: SN = 3.32

10 practice questions

0/10 correct

1.A higher SN withstands more

2.MR of subgrade is

3.Terminal PSI pt~2.0–2.5 is

4.a1=0.30, D1=4 in: contribution

5.Poor drainage m=0.8 reduces

6.Truck factor is ESALs per

7.Rigid (PCC) design uses

8.A 18-kip single axle is by definition

9.Reliability R and overall std So

10.Overlay SN needed is roughly