The thesis deals with the stiffness of soils at small strains. The analysis of excavation supported by the retaining diaphragm wall, for which horizontal movements with inclinometers were measured during and after construction, shows that small strain stiffness and its nonlinear dependancy on the strain amplitude should be properly taken into account to get reliable predictions of displacements. Finite element numerical analyses with computer program Plaxis were carried out taking into account two different material models: The nonlinear elasto-plastic model with isotropic hardening (Hardening Soil Model – HS model) and nonlinear elasto-plastic model with isotropic hardening and small strain stiffness (Hardening Soil Small Model – HSSMALL Model). The analyses were limited to the comparisson of bending moments and horizontal displacement of the diaphragm wall. The results of analyses, that consider HS model, show, that the bending moments and horizontal displacements are higher compared to inclinometer measured horizontal displacements. The HSSMALL model gives much better predictions as compared to the measured values of displcemants and therefore is more convenient for the analyses of such constructions.