A Flexible Pavement
1. A rigid pavement on a new interstate (3 lanes each direction) has been conservatively designed with a 12-inch slab, an Ec of 5.5 × 106 lb/in2, a concrete modulus of rupture of 700 lb/in2, a load transfer coefficient of 3.0, an initial present serviceability index of 4.5, and a TSI of 2.5. The overall standard deviation is 0.35, the subgrade CBR is 25, and the drainage coefficient is 0.9. The pavement was designed for 600 30-kip tandem axles per day and 1400 20-kip single-axle loads per day. If the desired reliability was 90%, how long was this pavement designed to last?
a) 18 b) 32 c) 42 d) 46
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. The reliability used was 90%, the overall standard deviation was 0.35, initial PSI was 4.7, the TSI was 2.5, and the soil resilient modulus was 2582 lb/in2. If the road has three lanes in the design direction (and was conservatively designed), for how many years was the pavement designed to last?
a) 12 b) 15 c) 20 d) 24
