Buffer blasting

BUFFER BLASTING

BUFFER BLASTING (EN: cushioned blasting; DE: Hohlraumschießen; FR: trous en libre confinement; ES: arranque por explosion amortiguada; RU: буферное взрывание) is the method for the blasted breaking, in case of which they preserve the portion of the rock (buffer), which has been shattered by the previous explosion, before the stope, which should be blasted.

The buffer blasting has been used for the first time within the USSR for the underground works during the 1953 (the mine breaking, and during the 1956, the borehole breaking). The support of the stope by the pressing material slows the sliding of the massif, which should be broken, and increases the duration of the action by the stresses, which have been caused by the explosion, which fact intensifies the shattering. The major problem for the calculation of the buffer blasting is the determination of the rational width for the buffer, which influences differently onto the degree of the shattering within the rocks, and onto the width of the burst of the rock mass after the explosion. The width of the buffer, which ensures the maximal usage of the energy from the explosion for the shattering, depends on the strength of the rocks, which are being blasted, and, at the open pit mines, amounts to 10-12 metres for the rocks with the intermediate and lower than intermediate strength, and amounts to 20-25 metres for the rocks with the high strength. The width of the burst from the rock mass during the buffer blasting, which is determining the quantity of the auxiliary works, is regulated by the parameters of the buffer. Within the rocks with the intermediate and lower than intermediate strength, the width of the buffer, which is excluding the burst, amounts to 20-30 metres, and within the rocks with the high strength, the width of the buffer amounts to 35-40 metres.

The buffer blasting has got the greatest distribution for the opencast development (see the Figure). Initially, the buffer blasting was used for the conducting of the cutting and capital trenches, and later for the breaking of the excavation blocks from the benches. They distinguish the buffer blasting onto the previously blasted rock mass, and the blasting within the absolutely pressed environment (onto the monolithic massif). The buffer of the shattered rock mass is created during the blasting onto the free surface of the massif, with the usage of the diagonal scheme for the wiring of the charges with the explosive substances. The buffer blasting is used for the development of the deep horizons within the open pit mines with the narrow working places on the benches. The effectiveness of the buffer blasting at the open pit mines is ensured in case of the blasting of at least four rows of the borehole charges, with the increased (up to 20%) specific consumption of the explosive substances within the first row of the boreholes.

The buffer blasting at the open pit mines ensures the improvement for the degree of the shattering for the rocks; the control over the burst of the rock mass during the explosion; the independence for the processes of the drilling, blasting, loading, and transportation; the possibility to conduct the selective excavation; the decrease of the non-productive downtimes of the equipment, and of the quantity of the auxiliary works, which are preceding the explosion; the increase of the quantities of the rocks, which are being exploded, and so on.

In case of the underground conditions, they perform the breaking and collapsing of the massif onto the clearing space, which is filled with the shrinked ore, or with the collapsed waste rock. The sliding of the pressing material near the stope after the explosion of the first row of the boreholes reaches 3 metres (in case of the blasting of 4-5 rows). The buffer blasting is used effectively for the breaking of the ore within the thick deposits, and within the deposits with the intermediate thickness, of the strong ores, and of the ores with the intermediate strength, and sometimes of the soft ores, for the decrease of the yield of the large lumps, for the increase of the productivity for the release and delivery of the ore (by 1.5-2.0 times); for the improvement of the stability of the massif; for the possibility of the shrinkage of the ore in case of the breaking along the vertical layers, and for the possibility of the release of the ore immediately into the drilling mine working.

Annually, at the iron ore open pit mines of the Krivbass, with the usage of the buffer blasting, there is broken up to 30-40 million cubic metres of the rock mass. The buffer blasting is distributed at many open pit mines for the extraction of the ores of the ferrous and non-ferrous metals (Sokolovsk-Sarbaisk and Kachkanarsk mining-beneficiating combined enterprises, and the Kalmakyrsk open pit mine, the flux open pit mines within Ukraine, and so on).