Evaluating orthotropic continuum analysis of stress wave propagation through a jointed rock mass

Abstract

Continuum modeling and discontinuum modeling are two approaches that are used to study the problem of stress wave propagation in jointed rock masses. In this study, a numerical analysis of blast wave propagation through a rock mass of three orthogonal joint sets was conducted by replacing the discontinuous media with orthotropic continua. The features of the simulated blast waveforms were fitted to those of the real seismograms (recorded at a distance of 300 m from a production blast at the Gol-e-Gohar iron ore mine) by iterative adjustment of the variable parameters. In order to account for the effect of rock joint dilation using the orthotropic elastic constitutive model, a search range was considered for the nonzero off-diagonal terms of the compliance matrix of the equivalent media, within which these three parameters were back-calculated independently. A simulated annealing search algorithm was used in conjunction with the numerical modeling to supervise the parameter adjustment. Finally, the response of the equivalent continuous model to dynamic loading was compared with the in situ records and the response observed in previously performed discrete modeling. The results demonstrated that the values of the peak particle velocities and the predominant frequencies in the model and those from site monitoring were in good accord. However, eliminating joints led to wider response Fourier spectra than seen for the real records and the jointed model results, and the numerical model required increased additional damping to compensate for this simplification.