Question

Using the AASHTO 1993 Flexible Pavement Design Procedure, design a pavement cross section that will provide 10 years service. The initial PSI is 4.2 and the final PSI is determined to be 2.5. The subgrade has a soil resilient modulus of 18,000 psi. Reliability is 95% with an overall standard deviation of 0.4. For design, the daily truck traffic consists of 400 passes of trucks with two single axles and 350 passes of semitrailer truck with tandem axles. The axle weights are:

Single-Unit truck                    =          8000-lb steering, single axle

                                                =          22,000-lb drive, single axle

Semiunit truck                        =          10,000-lb steering, single axle

                                                =          16,000-lb drive, tandem axle

                                                =          34,000-lbs trailer, tandem axle

M₂ and M₃ are equal to 1.0 for the materials in the pavement structure.

Answer 1

Single Unit Truck ESAL = 43.38 + 5.16 = 48.54

Semi Unit Truck ESAL = 43.38+ 6.00+7.4 = 56.78

So total ESAL's during design life = (400*48.54 + 350*56.78)*365*10/18000 = (19416+19873)*3650= 3939

Here

Reliability = 95% = 0.95, therefore ZR = -1.645, S0 = 0.4, MR = 18

Delta PSI = 4.2-2.5= 1.7

Resilient Modulus = 18000 psi, So MR = 18

Assume SN = 3.0 for flexible pavements

There W18 calculates to 0.26807

So

log10 (3939) = 9.36*log10(SN+1) -.2/(.4+1094/(SN+1)5.19)) -6.01

Structural Number SN = a1*d1 + a2*d2 *m2 +a2*d3 *m3

= a1*d1 + a2*d2 +a2*d3