Blast monitoring at a large open pit mine
Blast monitoring was undertaken at the Ekati Diamond Mine to investigate blast damage mechanisms in the mine's well jointed rock mass. Rock mass damage caused by production, pre-shear and wall control blasts was measured. Ekati utilizes 270mm holes for production blasting, and 165mm holes loaded with a decoupled charge for pre-shearing. The production blasts are loaded with bulk emulsion / ANFO blends. The mine plan involves using 30m double benches. A 30m high pre-shear is drilled and blasted prior to the production blasting that is done with sequential 15m benches. This paper is a summary of the monitoring equipment and data gathered to date.
Monitoring boreholes were placed within 5 to 10 m of the nearest loaded holes. A combination of geophones, borehole pressure sensors, and coaxial cables for time domain reflectometry were installed in the observation holes. Initial monitoring results indicate that gas penetration occurs when the pre-shear is detonated. Under pressures were also recorded in several of the pressure monitoring holes. The pre-shear appears to reduce the vibrations by as much as a third when compared to rock that has not been pre-sheared. The blast vibration data was used to develop scaled distance relationships for the site that will allow for the prediction of blast vibration levels and associated damage.
pre-shear, geophones, borehole pressure, Blast monitoring, decoupled, rock fracture, gas penetration