Constitutive equations for rock masses used in tunnel design

This paper describes the laboratory equipment and experiment program for the determination of the elastic/viscoplastic equations of Cristescu type, with associated/nonassociated viscoplastic potential. The experimental data needed for the derivation of these equations is obtained through triaxial tests on a MTS testing machine, using a triaxial cell. It is detailed the triaxial cell and the methodology for deformation measurements. The experimental program included both hydrostatic and deviatoric stress experiments. Based on laboratory experiments is determined the constitutive equation.