A sensitivity study and robustness evaluation of the CWFS and DISL approaches for brittle failure continuum modelling around underground excavations

• CWFS and DISL were assessed as approaches for brittle rock failure modelling. • Sensitivity analysis of the CWFS approach in FLAC indicates it is robust. • The DISL approach requires in-depth interpretation for its effective use. Numerical modelling of tunnels in brittle rock is a challenging endeavour for rock mechanics engineers. Multiple methods have been developed to aid in the design of underground excavations that are prone to brittle failure. For rock mechanics practitioners, the most useful tools are those that adequately and objectively represent the ground reaction, and can be interpreted without excessive qualitative judgement. With these goals in mind, continuum numerical models stand out amongst other methods. Two approaches that make use of continuum numerical modelling are the Cohesion Weakening Friction Strengthening (CWFS) and the Damage Initiation Spalling Limit (DISL) . To test their robustness, a sensitivity analysis of the strength parameters was conducted. The approaches were then applied to multiple fictitious stress scenarios to test their capability of reproducing empirical observations of depth of failure. The present investigation shows that the CWFS approach is a robust approach for modelling brittle failure around tunnels that can be easily applied and interpreted by rock mechanics practitioners. The sensitivity analysis of the CWFS parameters provided a full understanding of the practical impact of input parameter selection, some of which were not previously given in the literature. The DISL approach has been shown to also perform suitably, but requires the user to apply a fundamental understanding of numerical modelling for its effective interpretation.