Abstract: In this study, change in behaviors occurring beneath and around the foundation which caused by changes in foundation dimensions is studied numerically, by taking into account the interaction between earth and foundation. To do so, two dimensional and constant computational models with constant domain under uniform distributed load for both large and small foundation have been analyzed using ANSYS software, version 8.1. The results of this analysis clearly show that the earth beneath and around small foundations is shearing and general failure mechanism, which is the same as the predicted behavior and accepted failure mechanism most researchers believe in. But, based on the results obtained from this research, the earth located in the central areas as well as the earth under the large foundations is mainly bearing compressive and comprehensive stresses having hardening. Consequently, their endurance is gradually increasing. Hence, the stress concentrations as well as the deformations are directed toward this region. In case loading is constant, the regions outside the foundation and beneath (the sides) bear unloading (localization). While footing dimensions increase, rigid wedge angle will be increased up to 90°. Thus, the failure mechanism in large foundations is local and forming a resistant. Such resistance creates bearing column beneath the foundation and punching effect which happens between the earths under the vicinity of the foundation is clearly seen. Namely, if soil behavior and properties change, the foundation geometry will change as well. So, with regard to geometry increase and with the change in the behaviors of the earth material, the stiffness matrix changes which is in the form of coupled.