Application of Composite Geological Strength Index for healed rockmass structure to deep mine access tunnels
Rockmass characterization is an essential process for pre-construction geotechnical engineering design for underground excavations that requires an assessment of the macro-scale rockmass structure (interblock structure) and micro-scale intact rock strength to quantify rockmass behaviour. In complex rockmasses, meso-scale healed structure such as hydrothermal veins (intrablock structure) exists within rock blocks. When intersecting with excavations in deep environments, intrablock structure can have a significant influence on rockmass behaviour and should therefore be included in characterization. Methods to estimate the strength of a complex rockmass have been previously developed by the authors using a new Composite Geological Strength Index and validated with an adit case study at El Teniente porphyry mine. When the complex rockmass in the case study is encountered in the deeper undercut level, brittle failure occurs, which is not captured by shear-based GSI. This paper develops predictive tools to assess brittle behaviour of complex rockmasses using overbreak measurements and observations at the excavation scale.