Application of Rock Mass Rating system in underground intersections

Abstract

Rock Mass Rating (RMR) system has been applied in numerous civil and mining engineering projects. However, the applicability of the system in underground intersections has not yet been discussed. By creating an underground intersection, the only parameter of RMR that is affected is joint orientation favorability as the other five parameters (i.e. uniaxial compressive strength of rock material, joint spacing, RQD, groundwater condition and condition of joints) are not structural features but the intrinsic properties of rock mass. The suggested approach is based on considering the minimum rating for joint orientation favorability in the intersections as any set of discontinuity would be parallel or close to parallel with one of the openings in intersection. The application process and usefulness of suggested method is demonstrated by using it in selection of the most suitable location among 5 alternative options for starting a middle excavation face through an adit in the Alborz Tunnel Project. The case example shows that the method can be very helpful and important in practical applications of RMR system.