Tunnelling in rock depends on the ease or difficulty of rock removal when using different tunnel excavation methods. Excavability depends on the following rock properties: — Uniaxial compressive strength. — Hardness and abrasiveness. — Rock mass fracturing. — Geomechanical quality indexes. Uniaxial compressive strength and the spacing of discontinuities can be used to differentiate excavation by blasting from excavation by mechanical methods (Figure📸). An estimation of excavability for roadheaders, based on the uniaxial compressive strength, σci, and tensile strength, σt of rock, is as follows: — Easy to cut: σt/σci 0.1 Source : Nabaz Nooralddin, LinkedIn Source image: Nabaz Nooralddin, LinkedIn