Potential Impact of Blast Layout, Sequence and Detonator Timings on Air Overpressure from Blasting

摘要

Air overpressure (AOP) from blasting can give rise to a significant number of blasting complaints from residents living adjacent to blasting operations from mines, quarries or civil engineering projects. High amplitudes of AOP are usually associated with the lateral movement of a vertical free face, but it can also be caused by the upward lifting and the venting of gases through the surface of the blast area.rnPrevious work has shown that AOP levels can be related to scaled distance (in the form of m.kg-1/3 or lb.ft-1/3). However the initiation pattern of multi-hole blasts in terms of blast layout and the timing and direction of firing of the detonators can have a significant effect on the resulting peak AOP in certain directions around the blast. This is due to the constructive reinforcement of the air blast from particular holes which can occur given a certain geometry and timing. The inherent timing scatter of pyrotechnic delay detonators means that this is unlikely to occur very often, although some constructive reinforcement producing higher than expected AOP values can still occur.rnIt is generally accepted that the use of extremely accurate electronic detonators offers the chance to control ground vibration levels. However, caution must be exercised as there will be occasions where, due to the precision and accuracy of the detonator timings, certain combinations of blast layout and initiation pattern can give rise to zones or lines of significantly higher levels of AOP than would be expected. Where these lines of constructive reinforcement coincide with local residential properties, planning limits may be exceeded and/or complaints may be received from the local community.rnA simple calculator has been developed to allow potential issues to be identified at the blast design stage, thereby enabling simple mitigation methods such as changing the initiation sequence to be used to avoid generating maximum AOP values at third party properties adjacent to the blasting operations.