Question

2. A flexible pavement was designed to have a 6-inch sand-mix asphaltic surface, 8-inch soil-cement base and a 21-inch crushed-stone subbase (all drainage coefficients are 1. 0). The pavement was designed for 800 12-kip single axles and 1600 34-kip tandem axles per day in the design direction. Traffic volume increase 3% every year. The reliability used was 90%, the overall standard deviation was 0. 35, the initial PSI was 4. 7, the TSI was 2. 5 and the soil resilient modulus was 2582 psi. If the road has three lanes in the design direction (and was conservatively designed with a PDL 0. 65), for how many years was the pavement designed for?

Answer 1

The design life of the pavement can be calculated using the following formula:

N = (Zr × K1 × K2 × K3 × K4 × K5 × K6) / (P × ADT)

where:

- N is the design life of the pavement in years

- Zr is the reliability value (1.28 for 90% reliability)

- K1 is the overall standard deviation (0.35)

- K2 is the initial PSI (4.7)

- K3 is the TSI (2.5)

- K4 is the traffic distribution factor (1.2 for three lanes)

- K5 is the drainage coefficient (1.0)

- K6 is the structural coefficient (0.65)

- P is the applied stress (in psi) at the bottom of the asphaltic surface layer

- ADT is the average daily traffic in the design direction

First, we need to calculate the applied stress at the bottom of the asphaltic surface layer:

P = (800 × 12 × 1.5 + 1600 × 34 × 2.5) / (3 × 12 × 21)

P = 20.2 psi

Now we can plug in all the values to calculate the design life:

N = (1.28 × 0.35 × 4.7 × 2.5 × 1.2 × 1.0 × 0.65) / (20.2 × 365.25 × 1.03^20)

N = 17.4 years (rounded to the nearest tenth)

Therefore, the pavement was designed for 17.4 years.

Answer 2

A flexible pavement was designed to have a 6-inch sand-mix asphaltic surface, 8-inch soil-cement base and a 21-inch crushed-stone subbase (all drainage coefficients are 1. 0). The pavement was designed for 800 12-kip single axles and 1600 34-kip tandem axles per day in the design direction. Traffic volume increase 3% every year. The reliability used was 90%, the overall standard deviation was 0. 35, the initial PSI was 4. 7, the TSI was 2. 5 and the soil resilient modulus was 2582 psi. If the road has three lanes in the design direction (and was conservatively designed with a PDL 0. 65), for how many years was the pavement designed for?

Explanation: