ROYAL ORDNANCE, contractor Norwest Holst Soil Engineering and geophysical contractor Geo-Services International have joined forces to create an integrated ordnance detection service.
Surveys employ a new caesium vapour borehole magnetometer to record digital data that can be interpreted to detect unexploded bombs buried in the ground. False alarms common in 'noisy' (highly magnetic) ground are rendered less likely by modelling the data, which is not possible with analogue equipment.
'Traditional methods have relied on drilling a borehole 'blind' before using downhole geophysics to detect the unexploded ordnance, which could be disastrous,' says Royal Ordnance's Mike Sainsbury. He explains that as the new technique can detect ordnance in advance of the borehole, there is 'negligible chance' of accidentally detonating bombs.
Conventional borehole analogue magnetometers do not provide continuous records of the results and so there is no way of carrying out a verifiable risk assessment. They are limited to a detection radius of 1m and as they cannot be rotated in the borehole, blind spots can occur directly beneath them.
The new system is safer and more accurate, Sainsbury says, because it can survey in three dimensions, detecting objects up to 2.5m away. He adds that with increasing depth and low noise conditions, larger anomalies such as those formed by 500kg bombs can be detected up to 6m away.
The increased radius of detection also makes it more cost-effective, with fewer boreholes - four times fewer on a recent contract - needed for complete coverage.