Flexible Pavement Design (AASHTO Method)

We have prepared this info sheet to show the procedure for flexible pavement design using AASHTO method.

This info sheet shows essential charts engineers use to determine the pavement layer parameters and thickness.

Among those input parameters are layer coefficients (a1, a2 & a3) and drainage coefficient (m2 & m3).

Example of use is also provided in the nomograph we use to determine the structural number (SN).

Here we encounter a flexible pavement design problem.

We are required to determine the thickness of surface, base and subbase courses. The resilient modulus of each course is 400,000psi, 30,000psi and 12,000psi for surface, base and subbase respectively. The drainage coefficient is taken as 1 for base and subbase layer.

Some other relevant design parameters are design ESAL of 20 million, reliability of 95%, standard deviation of 0.3 and design serviceability loss of 2.0.

We can first determine the layer structural number from nomograph. The value of SN1, SN2 and SN3 are 3.2, 4.4 and 5.5 respectively.

Then, we define the layer coefficient by using their resilient modulus. They are found to be 0.42, 0.14 and 0.09 for surface, base and subbase layers.

Lastly, we can use these values to determine the layer thickness required.