The paper presents three methods of modelling of foundation stiffness beneath intermediate support of a 178 m long integral box girder viaduct and its impact on the values and distribution of displacements and internal forces in the pier of this support. The pier support is made of cast in situ reinforced concrete of strength class C50/60. For the analysis, three models were built in Abaqus FEA software [13]. The first model A3D in Figure 2a represents a complex three-dimensional model. The second L2D and the third H2D model shown in Figure 2b represent a simple two-dimensional models. The stiffness of the subgrade beneath the structure in the second and third model was modelled as spring constants calculated based on the equations given in the reference [8] model L2D and [10] model H2D. The middle range value of Young’s modulus for sand and gravel was used to calculate the subgrade stiffness parameters. In all models, a horizontal displacement in the Y direction of value 20 mm and a vertical force of value 18200 kN were applied to the top of the pier support. The horizontal displacement was caused by the thermal longitudinal expansion of the six-span viaduct deck and the braking force. The vertical force was caused by the dead, superimposed, and live loads acting on the viaduct deck. Finally, the values and distributions of displacements and internal forces in the pier support from the complex model were compared with the values in two simple models.