Design of Large-Scale Choked Destress Blasts in Mine PillarsUsing the Empirical Destressability Index Methodology

摘要

Some of the major challenges associated with underground mining at depth and/or under high extractionratios are related to the resulting high stress levels, which can lead to the failure and collapse of the rockmass surrounding the excavations. Sudden and violent failures, which can have severe consequences,represent the highest degree of difficulty in terms of underground personnel exposure, erratic andunpredictable production, ground rehabilitation requirements, possible reserve losses and overall miningcosts.There are a number of proactive and reactive measures that can be implemented to alleviate and mitigatethe problems associated with mining under high stress in general, and with violent failure in particular.One proactive measure that is given increasingly more attention consists in large-scale choked (with nofree face) destress blasts aimed at altering the local stress regime by damaging the rock mass.This paper provides an update on a developed empirical methodology that has been successfully used toquantify the likelihood of success of large-scale choked destress blasts in underground mine pillars, forgiven sets of rock mass conditions and stress regime. This methodology is based on the “DestressabilityIndex”, which considers four geomechanical parameters (the stiffness, brittleness, in situ degree offracturing and proximity to static failure of the rock mass) and four blasting parameters (the orientationand width of the blast, unit explosive energy, and charge confinement), which were found to ultimatelycontrol the destressing process.The back-analysis of well-documented case studies, as well as the application of the “DestressabilityIndex” in the design of destress blasts have demonstrated the validity of this approach. It has beendemonstrated that it can indicate whether a given situation is conducive to being destressed by means of alarge-scale confined destress blast, and, if so, whether the blast design itself is appropriate to achieve thisgoal.