LARGE DEFORMATION THEORY IN GEOMECHANICS - INFLUENCE OF KINEMATIC NONLINEARITY ON THE RESULTS OF SOME CHARACTERISTIC GEOTECHNICAL CALCULATIONS

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

Deformation anisotropy of soft rock

Slojevitost kao tipično svojstvo sedimentnih stijena, uzrok je inherentne anizotropije deformacijskih svojstava stijenskih masa. Rezultati jednoosnih i troosnih, kratkotrajnih i testova puzanja provedenih od strane autora na orijentiranim uzorcima meke sedimentne stijene - lapora prezentirani su u ovom radu. Interpolacijom rezultata kratkotrajnih pokusa utvrđena je parabolična ovisnost sekantnog modula deformabilnosti o kutu (a) između opterećnja i ravnine prirodne slojevitosti u intervalu od 0 do 90 stupnjeva. Vremenski ovisan deformacijski odgovor je opisan utvrđivanjem ovisnosti parametara modificiranog Wallnerovog modela o kutu a u intervalu od 45 do 90 stupnjeva na osnovi rezultata provedenih testova puzanja.Bedding, being a typical feature of sedimentary rocks, is a cause of inherent anisotropy of deformation properties of rock mass. Results of uniaxial and triaxial, short-term and creep tests conducted by the authors on the specimens of a soft sedimentary rock - marl are presented in this paper. Interpolation of results of the short-term tests enabled for determining the parabolic dependence of secant modulus of deformability on angle (a) between load and natural bedding planes in the interval from 0 to 90 degrees. The time-dependent deformation response is described by determining the dependence of parameters of the modified Wallner’s model on the angle a in the interval from 45 to 90 degrees, based on the results of the performed creep tests