The discontinuities are main factor on discontinuous, anisotropic, and non-elastic behavior of rock mass. The objective of this paper is to present a new discontinuity rating system called “Universal Discontinuity index” (UDi), based on the combination of quantitative and measurable parameters of the discontinuity network, damage mechanics, vectorial based criteria of Warburton for kinematic rock block failure analysis, and Mohr-Columb criteria for shear failure analysis. Applying the UDi permits to capture the heterogeneous and anisotropic nature of the rock mass strength or equivalently the degree of damage. A new, simple, and fast procedure for logging geomechanical drill cores is proposed, which allows UDi to be applicable at every stage of rock engineering projects. We used the UDi for the prediction of the spatial geometry of over-excavation along a tunnel. There is a good agreement between the variational trend computed using UDi and over-excavation along a tunnel observed at El Teniente mine, Chile. Moreover, the good correlation between rock mass quality rating from UDi and Rock Mass index (RMi) demonstrate the reliability of the UDi rating system.