Blast Vibration Monitoring and Elastic Wave Refl ection Models to Assess Blast-Induced Damage to Mine Infrastructure – An Underground Case Study

摘要

During underground mining, rock mass changes can occur as a function of the mining sequencernand excavation processes. Mining-induced rock mass damage can occur due to redistribution ofrnstatic stresses and the application of dynamic stresses from blasting and seismic activity. Thesernrock mass changes can result in a degradation of strength of the bulk rock mass and the remainingrnrock surrounding existing excavations. Rock mass damage near existing excavations which lead tornexcavation-scale instabilities such as rock fall, excavation closure, or visible rock mass fracturing canrndetrimentally affect the safety and profi tability of mining operations.rnThe focus of the current work was the prediction and assessment of damage to mine infrastructurernoccurring in relation to the blasting of a sublevel open stope. The study case involved a 60kt stopernlocated in a highly-competent rock mass at a large Australian sublevel open stoping mine. The minerninfrastructure of interest for investigation included local stope access development, critical accessrnand haulage development crossing a regional-scale fault, an explosives storage magazine and arnventilation return air raise. The methods used to predict or assess the blast-induced damage to eachrninfrastructure element in response to stope extraction were:rn? intact rock strength testing,rn? discontinuity mapping,rn? linear-elastic static stress modelling,rn? blast-damage mapping,rn? near-fi eld blast vibration monitoring and analysis,rn? geophysical assessment using inferred stiffness and wave velocity methods, andrn? post-extraction void assessment.rnThe results of the detailed blast damage prediction and assessment program at the mine site havernbeen discussed by the primary author elsewhere (Fleetwood, 2010). The current work will addressrnblast-induced damage to mine infrastructure as a result of extraneous blasting vibrations from stopernproduction blasting. A method for predicting the amplifi cation of excavation surface motions fromrnrefl ecting body waves will be discussed as well as the results of damage mapping around the studyrnstope. The results of the damage mapping program identifi ed blast-induced damage that occurredrnto the surface of the explosives storage magazine and local stope access development. No damagernwas observed at the main fault crossing or return air raise where higher vibration amplitudes werernmeasured or predicted.