In this method of pavement design, we use the Tri-axial shear test to determine the Elastic modulus of the sub-grade material or those of the other layers. Boussinesq’s equation is used to determine the thickness of the pavement.
In order to include the factors, amount of traffic and rain-fall ‘X’ and ‘Y’ are multiplied to the equation which gives us the pavement thickness. More the traffic and amount of rainfall higher will be the values of ‘X’ and ‘Y’.
A stiffness factor is introduced when the Elastic moduli are different for the sub-grade and pavement layers. This factor (Es/Ep)**(1/3) is multiplied to the former value of thickness in which, the moduli are considered equal.
In order to find out the thickness for the different layers, we simply use the stiffness factor according to which, the thickness is inversely proportional to the Elastic modulus raised to a power of 1/3.
