Determining the Relative Influence of Joint and Rock Properties on the Propagation of Planar Waves in Jointed Rock Masses Using Multivariate Statistical Techniques

The effect of discontinuity stiffness and spacing and intact block stiffness on the transmission of stress waves through a rock mass has been assessed with the use of a large database of 1531 analysis results, generated using a 1D numerical model. This was undertaken by modelling different jointed rock masses as a discontinuum in the Universal Discrete Element Code, UDEC. The discontinuous rock masses were modelled using the Mohr-Coulomb constitutive model for rock blocks and the Coulomb area model applied to discontinuities. Multivariate statistical techniques were used to determine a best fit relationship between the input parameters of the rock mass and rock mass transmission. The factors influencing wave transmission in jointed rocks were subsequently assessed. It was found that joint stiffness has a greater effect on the transmission of stress waves than joint spacing or intact block stiffness. The input wave frequency was also found to have a large effect on transmission. When wave transmission is viewed in the context of high speed rail trains in tunnels it can be concluded that high frequency vibrations, brought about by dynamic loading, are unlikely to be transmitted through a jointed rock mass.