Introduction Among many different approaches to determine of the bearing capacity of shallow foundations, the well-known formula of Karl Terzaghi (1943) has been widely accepted for the bearing capacity as follow [1]: (1) In this equation, q ult is the ultimate bearing capacity, c is the soil cohesion, q is the surcharge pressure, B is the foundation width, γ is the soil density, and the N i coefficients are the bearing capaci- ty factors as functions of soil friction angle. The third term has been known as the main contributor in the bearing capacity of shallow foundations, however, unlike the first two factors, i.e., N c and N q , the third factor is the most challengeable one. There are several values for the third factor suggested by dif- ferent authors [1-7]. Although all of these methods are generally based upon a limit analysis solution, there are differences between their assumptions on the boundary conditions and taking the effect of soil weight into account. It is also remarkable that the bearing capacity of shallow foundations is computed based on an associative flow rule assumption. There are a few studies on the nonassociative flow rule effect on the bearing capacity. Michalowski (1997) showed that, in general, such assumption results in a lower bearing capacity factor, N γ [6]. 0.5 . ult c q q cN qN BN γ γ = + + Soil Mechanics and Foundation Engineering, Vol. 47, No. 3, 2010 There are a number of factors affecting the bearing capacity of shallow foundations. Among them, the scale effect can be mentioned as one of the most important factors. Unlike the theoretical equations, experiments show that the bearing capacity of founda- tions does not increase without limit when the foundation size increases. The effect of stress level on soil shear strength parameters has been known as the main reason for this observation. The method of the zero extension lines (ZEL) for the solution of plasticity problems in soil mechanics has been utilized to take this effect into account by incorpo- rating the stress level − dependent soil friction angle. The bearing capacity of shallow foundations is then computed with the aid of this method, showing a decreasing tenden- cy in the third factor, N γ , which is the main contributor in shallow foundations. Compar- isons have been made with experimental data, showing good consistency between experi- ments and theoretical predictions with the ZEL method. APPLICATION OF THE ZEL METHOD IN THE PREDICTION OF FOUNDATION BEARING CAPACITY CONSIDERING THE STRESS LEVEL EFFECT M. Veiskarami, M. Jahanandish and A. Ghahramani Shiraz University, Shiraz, Iran UDC 626.862 SOIL MECHANICS Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 2-7, May-June, 2010. 0038-0741/10/4703-0075 © 2010 Springer Science+Business Media, Inc. 75