The understanding of the grout deformation and failure process and the use of appropriate constitutive models are the basis to predict the behavior of grouted threadbar, commonly used in Chilean mining as reinforcement in underground excavations during dynamic loading. Based on results from triaxial tests the authors have captured the essential components of grout failure, that are, cohesion weakening and frictional strengthening (CWFS) and mobilized dilation angle as function of plastic strain. After this procedure a consistent parameter set for the strain-hardening /softening Mohr-Coulomb constitutive model was implemented in numerical modeling software FLAC3D. The good agreement between numerical and laboratory results indicates that the mechanical properties of the grout and its variation are well suited to represent the nonlinear mechanical behavior of grout especially in the post-failure region. Finally, a proposal of a numerical model for dynamic laboratory testing, where the grout calibration will be used is presented.