In order to satisfy environmental and mine operational requirements it is
becoming increasingly important to minimise ground blast vibrations at
certain locations. These locations are often in soil or on large resonant
structures such as grain silos, highway bridges or even the walls of an
open pit. A soil monitoring exercise was carried out to evaluate the common
practice of coupling vibration detectors to the ground using spikes. At a
series of locations in an operating quarry the spiked array response to
single blastholes was compared with that of an accelerometer array
attached to a calibrated embedded mount. The results clearly showed that
the spiked arrays over-estimated the true ground vibration by 46.5 per
cent on average, with a maximum observed error of 99.2 per cent. These
errors are considered too large for compliance monitoring where accurate
vibration levels are required for comparison with prescribed limits.
Although spike coupling is convenient, its use for compliance monitoring
should be viewed with caution. Unfortunately, however, many
manufacturers supply their detectors as spiked arrays. A structural monitoring exercise was also carried out to evaluate the
vibration response of a grain silo, highway bridge and a pit wall to the
initiation of single blastholes. In this case accelerometers and standard
geophones were firmly attached to the bridge which resonated at low
frequencies. The results clearly show that, due to their limited
low-frequency response, the geophones typically measured only half the
true vibration level as measured by the accelerometers.