Development of a comparative index for the assessment of the severity of violent brittle failures around underground excavations

In order to assess the severity of a violent brittle failure (strain-burst) around the vicinity of complex underground excavations an index parameter has been developed. The index incorporates measures of the induced stress path and accumulated plastic strain and is calculated after brittle failure conditions are identified by the established Damage Initiation Threshold and Spalling Limit (DIT-SL). The comparative index developed provides guidance to minimize strain-burst hazard for geotechnical design. Application of the index to a conceptual model shows that strain-burst hazard can be related to geological boundaries and their exposure in excavation faces. The potential violence of these strain-burst failures can be quantified by changes in principal stress and plastic strain within a numerical model.