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

To determine the thickness required for the base if soil cement is the material to be used, calculate the equivalent single-axle load (ESAL) using the axle weights and the number of passes for each type of vehicle. The total ESAL per day is 229,075 kip. Using the design equation, the thickness of the base is approximately 0.689 inches.

Step-by-step explanation:

To determine the thickness required for the base if soil cement is the material to be used, we need to calculate the equivalent single-axle load (ESAL), which represents the total effect of all traffic loads on the pavement. We can calculate the ESAL using the axle weights and the number of passes for each type of vehicle.

1. First, let's calculate the ESAL for the car, pickup truck, and light van traffic. Each vehicle has two 2 kip single axles, so the total load per vehicle is 4 kip. The daily traffic is 40,000 vehicles, so the total load is 40,000 * 4 = 160,000 kip per day.
2. Next, let's calculate the ESAL for the single-unit trucks. Each truck has an 8 kip single axle and a 24 kip single axle. The daily traffic is 1500 trucks, so the total load is 1500 * (8 + 24) = 48,000 kip per day.
3. Finally, let's calculate the ESAL for the tractor semi-trailer trucks. Each truck has a 10 kip single axle, an 18 kip tandem axle, and a 42 kip triple axle. The daily traffic is 325 trucks, so the total load is 325 * (10 + 18 + 42) = 21,075 kip per day.

Now, we can calculate the total ESAL per day by summing the loads from each type of vehicle: 160,000 + 48,000 + 21,075 = 229,075 kip per day.

To design the pavement to last 10 years with a reliability of 95%, we need to determine the thickness required for the base using the design equation:

H = [(Zr * So) / (N * E * C * Pi)]^(1/(m+1))

Where:

• H = Thickness of the base
• Zr = Z-value for the desired reliability, in this case 1.645 for 95% reliability
• So = Resilient modulus of the subgrade soil, 15,000 lb/in^2
• N = Number of ESALs per day, 229,075 kip/day
• E = Overall standard deviation, 0.35
• C = Average vehicle damage factor, assuming 2 and 3 are equal to 1
• Pi = Pressure imposed by the tire contact, assuming 1
• m = Slope of the resilient modulus

Plugging in the values, we have:

H = [(1.645 * 15,000) / (229,075 * 0.35 * 1 * 1)]^(1/(0.35+1)) = 0.689 inches

Therefore, the thickness required for the base if soil cement is the material to be used is approximately 0.689 inches.