Rational methods are based on the formulation of the elastic problem in soils. The criterion focuses on limiting the maximum deflection that occurs at the end of a road pavement's service life. Generally, the adequacy of a road pavement is expressed through the following safety measure:
Where fadm is the allowable deflection that the road can withstand over its useful life, while fd is the calculated deflection on the designed road. The RPD software implements two types of verifications using the rational method:
- Ivanov's method;
- Westergaard's method.
The Ivanov method (also known as the maximum deflection method) is based on Boussinesq's formulation of the elastic problem in soils. The criterion focuses on limiting the maximum deflection that occurs at the end of a road pavement's service life. Further details on the calculation of the terms contributing to estimating the adequacy of road pavement using the Ivanov method can be found in the document THE CALCULATION OF ROAD PAVEMENT USING THE DEFLECTION METHOD.
The Westergaard method is used to solve the Lagrange equation for thin plates. From a general perspective, the method is thus a tool for calculating the maximum deflection to which a layered thin plate (approximated as the road pavement) is subjected. The verification (or design) criterion is analogous to that on which the maximum deflection method is based. Further details on the calculation of the terms contributing to estimating the adequacy of road pavement using the Westergaard method can be found in the document RATIONAL CALCULATION OF ROAD PAVEMENT USING THE WESTERGAARD METHOD.