The primary objective of this paper is to present new methods in characterising flexible pavements that possess nonlinear subgrade behavior using deflection data from falling weight deflectometer (FWD). The two techniques to be introduced are Simplified Deflection Modeling and Deflection Ratio (DefR) approach. FWD deflection data can be modelled accurately using an exponential curve in a mathematical form of Y = K1 exp (−r/K2). K1 is equal to deflection at D0 in micron and K2 is the structural parameter at the respective sensor location. K2 parameter is found to have a direct relationship with the material constant, value of the subgrade and it is taken as a measurement of the nonlinearity of the pavement layer. As K2 increases and approaches 500, the pavement structure is observed to possess linear elastic behaviour. In the second method, the DefR is defined as the ratio of the FWD deflection of a sensor divided by the deflection of the preceding sensor. For pavements that exhibit nonlinear subgrade behavior, the DefR shows an increasing trend for FWD sensors located at 300mm and beyond. The two techniques have provided alternative approaches for modelling subgrade nonlinearity.