Question

Using the AASHTO procedure, determine the thickness required for a base and a surface layer over existing subgrade. The structural number required for this pavement is 4.5. The available materials are a crushed stone base course with a material layer coefficient of 0.13 and an HMA surface with a material layer coefficient of 0.40. The drainage coefficient of the based course can be considered as 0.90.

Answer 1

Answer:

the thickness required would be 12 inch HMA and granular base layer of 6 inches

Explanation:

structural number = 4.5

stone base course material coefficient = 0.13

hma material layer coefficient = 0.40

drainage coefficient = 0.90

we will use layered analysis procedure to get thickness

D1 >= sN1/a1

when we cross multiply,

sN1 = a1D1 >=sN1

D2 >= -sN2-sN1/a2m2

sN2* + sN1* >= sN2

D3 >= sN3-(sN1*+sN2*)/a2m2

where a1,a2,a3 = layer coefficient

d1 d2 d3 = actual thickness

m2,m3 = coefficient of base

a1 = 0.4

a1 = 0.13

sN = 4.5

m2 = 0.9

D1 >= sN1/a1 = 4.5/0.4

= 11.25

thickness of surface = 12 inches

a1D1 = 0.4x12 = 4.8

we have value of sN2 = 5.5

(5.5 -4.8)/(0.13*0.9)

= 0.7/0.117

= 5.9829 inches

approximately 6 inches

so the pavement will have 12inch HMA surface and 6 inches granular base layer.