Standard Deviation

1. A flexible pavement is constructed with 5 inches of sand-mix asphaltic wearing surface, 9 inches of dense-graded crushed stone base, and 10 inches of crushed stone subbase. The base has a drainage coefficient of 0.90, while the subbase drainage coefficient is 1.0. Determine the SN of the pavement.

a) 4.47 b) 4.31 c) 4.76 d) 3.98

2. A flexible pavement is designed to last 10 years to withstand truck traffic that consists only of trucks with two 18-kip single axles. The pavement is designed for a soil CBR of 2, an initial PSI of 5.0, a TSI of 2.5, an overall standard deviation of 0.40, and a reliability of 90%, and the SN was determined to be 6. On one section of this roadway, beneath an underpass, an engineer uses a 10-inch rigid pavement in an attempt to have it last longer before resurfacing. How many years will this rigid- pavement section last? (Given the same traffic conditions, modulus of rupture = 800 lb/in2, modulus of elasticity = 5,000,000 lb/in2, load transfer coefficient of 3.0, and drainage coefficient of 1.0.)

a) 11.33 b) 13.22 c) 17.14 d) 25.65

3. A flexible pavement at an access road to a sports stadium parking lot is designed with a 4-inch sand-mix asphaltic concrete surface, 5-inch aggregate bituminous emulsion base, and a 10-inch crushed stone subbase. There are 95 scheduled baseball and football games at the stadium per year. The access road to the parking lot is three lanes in each direction (conservatively designed). The pavement was designed for recreational vehicles with one 20-kip single axle and one 20-kip tandem axle. There are 9000 recreational vehicles estimated at each event. Given that drainage coefficients are 1.0, the overall

standard deviation of traffic is 0.45, reliability is 90%, and the soil’s resilient modulus is 15,000 lb/in2, how many years will the access road last if the initial PSI is 4.0 and the TSI is 2.5?

a) 7 b) 9 c) 12 d) 14