The functionality requirements for modern railway tracks lead to the use of performance based specifications regarding the quality control of substructure layers. Those specifications require the construction of the layer to be evaluated through specific tests to be performed under different state conditions, in order to estimate material properties, namely deformability modulus. The Surface Web Method (SWM) has been used in a research work during the renewal of a Poruguese railway line platform (Nothern Line), in which minimum values for deformability modulus at the top of capping and sub-ballast layers were specified. This paper presents some aspects related with the application of this method and some results obtained. The results are discussed and both the adventages and the disadventages of the method are identified