Influence of distance in the effective use of electronic detonators to control blast induced ground vibrations

摘要

The use of electronic detonators to control blast vibrations has been previously established by many authors. This is performed by determining the optimum delay period between the blast holes for a particular pattern that can accurately control the firing frequency of the blast, which in turn has a direct bearing on the frequency composition of the ground vibrations recorded at a particular location. This was established by Pedgen, Birch, Hosein & Farnfield (2006) whereby like-for-like comparison tests between non-electric and electronic blasts were carried out in a limestone quarry in northern England. They demonstrated that resulting peak particle velocity values recorded at near and mid-field distances were primarily a product of the firing frequency of the electronically initiated blasts.However, it was thought that distance may also be another controlling factor in the deployment of electronic donators. The logic being that, all frequencies dissipate as the distance increases from any given blast to an observation point; however the controllable frequencies being of the order of 15 to 200 Hertz will attenuate in a shorter distance than 1 to 8 Hertz. This is also compounded by the fact that the actual blast vibration consists of a number of different wave types. The two main wave types are body waves and surface waves. These in turn also attenuate at different rates due to geometric spreading; the surface wave in proportion to the reciprocal of the distance (1/r) and the body wave in proportion to the reciprocal of the square of the distance (1/r~2).A series of like-for-like comparison tests between non-electric and electronic blasts were carried out in a chalk quarry where the recording distances covered was over 1km. It was found that the controllable frequencies appeared to be contained within the body waves produced by the blast. However once the body waves have dissipate, the surface wave was found to be still present and (due to its low frequency content and slower propagation velocities) the vibration travelled great distances from the blast. The analysis indicated that when plotting "Scaled Distance" verses the Peak Particle Velocity, there appeared to be two separate sections to the graph. At close distances the firing frequencies were found to present and thus the actual PPV levels could be modified. However at far distance these specific frequencies no longer dominated the vibration trace and thus it was no longer possible to modify the PPV levels produced by the blast.