Holistic scientific approach to address wall damage and berm loss from blasting in large open cut metal mines

摘要

Highwall failures in large deep open cut mines have very significant safety andcommercial implications. There are many factors influencing the stability ofhighwalls. The major influence is the interaction of the local geology with the shapeof the pit wall. This factor is in the realm of the geotechnical engineer and is beyondthe control of the blasting engineer. However, a secondary influence is the blastinduceddamage to the wall. In most open cut metal mines the blasting strategy tocontrol this damage involves the use of separate production and trim blasts boundedby presplits at the final wall.Many mines adopt a quality control approach to blasting which may be complementedby trial and error attempts to improve outcomes. However this generally leads to onlyincremental adjustments in blast parameters and does not always lead to success inaddressing more complex problems like wall control. Furthermore, such trial anderror approaches often result in a lengthy improvement program that requires a largeamount of the engineering resources and is thus not sustainable. As a result, wall andberm failure continue to be major threats for deep open cut mines.This paper discusses a holistic scientific approach to address blasting-related walldamage issues by measuring major contributing factors and using the latesttechnology and blast models to reduce their impacts. The applications of blastvibration modelling and borehole pressure measurements are each discussed in detail.A new multiple layer method of blasting for vibration control is presented, wherebyseparate blast layers are fired with a long, multisecond delay between the layers. Thisenables complete separation of vibration waveforms emanating from each layer andleads to overall reductions in vibration.Combining wall control blasts with production blasts in a single blast event can alsomake substantial productivity gains. Provided sufficient understanding of blastdamage mechanisms has been gained, appropriate design modifications can result inincreased productivity with lower cost and improved wall control outcomes.