Performance of conventional numerical modelling of brittle rock failure in underground openings: is cohesion weakening–friction strengthening approach the only solution?

A cohesion weakening–friction strengthening (CWFS) approach has been developed and modified by several researchers and explained to aim to simulate brittle failure more successfully compared to traditional numerical analysis techniques with peak-residual strength envelopes and elastic-brittle-plastic approach. Some research questions the simulation performance of traditional techniques and this research considers some underground opening cases which are analysed by the CWFS approach for the analysis of brittle failure conventionally. The traditional analyses are carried out by using an implicit finite-element analysis programme by employing typical elastic-brittle-plastic behaviour. The results revealed that the typical Mohr–Coulomb and generalised Hoek–Brown failure criteria used in the form of elastic-brittle-plastic behaviour are capable of simulating brittle failure in underground openings. Currently, a retirement for traditional concepts is found to be too early since there are some discrepancies in the new approach in this field. CWFS parameters are investigated in this research for the well-known mine-by tunnel case in Lac du Bonnet case with granite parameters that offer either an elastoplastic material model indirectly or a problematic fluctuation in low confinement. The analyses reveal that traditional methods are also capable of capturing brittle failure, especially from the engineering practice aspect.