Question

A flexible pavement is to be designed to last 10 years. The initial PSI is 4.2 and the TSI (the

final PSI) is determined to be 2.5. The subgrade has a soil resilient modulus of 15,000 lb/in2

.

Reliability is 95% with an overall standard deviation of 0.35. For design, the daily car,

pickup truck and light van traffic is 40,000 and the daily truck traffic consists of 1500 passes

of single-unit trucks with two single axles and 325 passes of tractor semi-trailer trucks with

single, tandem, and triple axles. The axle weights are:

• Cars, pickups, light vans = two 2 kip single axles

• Single-unit truck = 8 kip single axle and 24 kip single axle

• Tractor semi-trailer truck = 10 kip single axle, 18 kip tandem axle, and 42 kip triple

axle.

??2 and ??3 are equal to 1 for the materials in the pavement structure. Four inches of hot-

mix asphalt (HMA) is to be used as the wearing surface and 10 inches of crushed stone as

the subbase. Determine the thickness required for the base if soil cement is the material to

be used.

Answer 1