Journal of Applied Sciences1812-56541812-5662Asian Network for Scientific Information10.3923/jas.2009.4006.4012Ziaie-MoayedR.JanbazM.122009922In Winkler model the subgrade soil is assumed to behave like infinite numbers of linear elastic springs, which the stiffness of the springs is named as the modulus of subgrade reaction. This modulus depends on some parameters like soil type, dimension, shape, embedment depth and type of foundation (Flexible or Rigid). The direct method to estimate the modulus of subgrade reaction is the plate load test. In this study the foundations on clayey soil are modeled with finite element software to investigate the validation of Terzaghi’s formula and the effect of different parameters on subgrade reaction modulus. Due to obtained results, Terzaghi's formula does not consider the effect of soil consistency and the shape of foundation; therefore it results in uncertain values. As depth of embedment of foundation is increased, the modulus of subgrade reaction is increased. Flexural rigidity of foundation can improve the status of subgrade reaction modulus.]]>Biot, M.A.,1937Bowles, J.E.,1997Consoli, N.C., F. Schnaid and J. Milititsky,1998Filonenko-Borodich, M.,1940Hetenyi, M.,1946Horvath, J.S.,1983Horvath, J.S.,1983Pasternak, P.L.,1954Terzaghi, K.,1955Daloglu, A.T. and C.V.G. Vallabhan,2000Vallabhan, C.V.G. and T. Daloglu,1999Vallabhan, C.V.G. and Y.C. Das,1989Vlasov, V.Z. and N.N. Leontev,1960Winkler, E.,1867Vesic, A.S.,1961