Question

A rural principal arterial is expected to carry an ESAL of 0.188 × 10^6 during the first year of
operation with an expected annual growth of 6% over the 20-year design life. If the subgrade has a
resilient modulus of 15,000 lb/in2, design a suitable pavement consisting of a granular subbase with a
resilient modulus of 13,500 lb/in2, a granular base layer with a resilient modulus of 25,000 lb/in2, and
an asphalt concrete surface with an elastic modulus of 400,000 lb/in2. Assume all mi values = 1 and
the percent of traffic on the design lane is 47%. Assume a reliability level of 95%, the design
serviceability loss is 2.0, and standard deviation of 0.4.

Answer 1

Solution:

Given that:

ESCL = 0.188*10^6

Annual Growth =6%

Design life = 20yers

Subgrade of resilient Modulus =15000lb/in2

Asphalt Concrete Modulus =400,000lb/in2

layer cofficient : Subbase =13,500lb/in2

base layer = 25,000lb/in2

Standard deviation =0.4

Reliability=95%

Serviceability loss = 2.0

Total ESAl = fd*Gm*expected ESAL

fd design lone factor =0.47

G growth factor = 36.79(for 20years)

Total ESAL = 0.47*36.79*0.188*10^6

= 3.24*10^6

Calculate the depth of subbase O3

Use the monograph to verify the structural number

SN =40

From char for eliminating strucutral layer coefficient of Asphast concrete E =400,000lb/in2

a1 = 0.40 and a2 = 15,000lb/in2 ,a3 = 13,500lb/in2

From Table AASTHO Recommended minimum thickness of highway layer

For 3.24*106 ESAL

D1 - Asphast concrete thickness = 3.5in

D2 - Aggregate base thickness = 6in

m2 =1 , m3 =1

4 =0.40*3.5+15000*6*1+13500(D3)1

4 =1.4+90000+13500D3

D3 = 90001.4 / 13500

D3 =6.7in

Depth of sub base = 7in

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