The geotechnical engineering calculations are usually carried out according
to the small deformation and displacement theory (infinitesimal strain
theory) i.e. first-order theory. A linear relationship between componental
displacements and deformations is adopted. The well-known conditions for
equilibrium are defined for an undeformed system i.e. undeformed structure.
Therefore, the geometric and static linearity assumptions are usually valid
in geotechnical engineering calculations. These linearities are collectively
referred to as kinematic linearity. In other words, engineers believe that
results of quite satisfactory accuracy are obtained if only material
nonlinearity is taken into account in the engineering calculations,
regardless of the type of geotechnical problem being analysed. Therefore, it
is not necessary to apply the large (finite) deformation theory with the
assumption of material nonlinearity. The main aim of this paper is to verify
the previous statement in the case of some characteristic problems of
Geotechnics. In the first part of this paper, the large deformation theory,
which is mostly unknown to the wider professional public, is briefly
presented. After that, simple numerical analyses of some characteristic
problems of Geotechnics were carried out in the well-known software FLAC 2D
software with the aim of comparing the results obtained for the cases of
kinematic linearity and kinematic nonlinearity. The obtained results point
to the fact that kinematic nonlinearity should not always be ignored in the
usual geotechnical engineering calculations. Therefore, engineers are urged
to be careful.