How it works

The EM61 is an instrument using electromagnetics to detect buried metal targets. It does this by discriminating between moderately conductive soils and very conductive metallic targets.

The instrument consists of a horizontally carried loop transmitter and receiver. There is a secondary receiver mounted over the primary loop to allow target depth estimates to be made, as well as help reject near surface target responses. The transmitter generates 150 electromagnetic (EM) pulses per second while the receiver measures the induced secondary EM field during the time between pulses. The secondary EM fields will last a moderate time in conductive soil and for a longer time in metallic targets, The EM61 ignores the earth responses and measures the prolonged buried metal response. The instrument incorporates a data logger so that the prolonged EM responses are recorded together with the co- ordinates so that an areal plot of the survey can be made.

The EM61 is a quick and effective geophysical method of locating metal objects buried to depths of up to 3m including:

• Underground storage tanks
• Buried drums
• Reinforced foundations and piles
• Pipelines
• Cables
• Metal waste and unexploded ordnance

Large areas can be covered in one day with the added benefit of quick processing to pinpoint areas of interest.

Case study

A large area of concrete slab was being considered for part of a development project. In particular it was hoped that the existing piles, pile caps and ground beams could be reused. In order to assess this it was necessary to locate the piles and their associated caps and ground beams. The EM61 survey reproduced here shows the layout of these foundations enabling further investigations to be made.