Oftentimes, static analysis of a slab supported by vertical uncoupled Winkler springs is frequently utilized in the structural design of shallow foundations. Many structural designers typically simulate the soil beneath the footing and the raft as a collection of springs with stiffness coefficient estimated based on the modulus of subgrade reaction (ks). Therefore, various approaches for determining ks are compared and reviewed in this work. 
   The main objective of this study is to estimate the modulus of subgrade reaction (ks) of the shallow foundation rested on sandy layer adopting three constitutive soil models (Elastic, Mohr-Coulomb and Hardening soil) utilizing 3D Plaxis analysis. Two parametric studies have been implemented (isolated footing and raft) taking into consideration the effects of foundation thickness and soil constitutive model on ks. 
   The results outlined in this paper show that a thicker footing typically has a lower soil subgrade reaction than one that is thinner; and the estimation of ks based on empirical formulas is being convenient in case of isolated footing. On the other side, the distribution of ks is non-uniform through the raft for all adopted soil models analyses. ks (when considering soil plasticity) is lesser than ks estimated using elastic soil analysis. Using non-linear finite element analysis (considering the soil plasticity) is very important to get more accurate ks and do not depend only on the empirical formulas to evaluate ks of the raft.