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Technical paper: Sub-surface investigation for shallow mine workings and cavities by the ground impulse radar technique

By Peter Leggo, Cambridge House Geotechnical Services and Chris Leech, Geophysical and Scientific Equipment


In a recent article by Darracott and Lake careful description of the ground radar technique was presented together with several case histories. This work clearly demonstrates the potential of the new radar technology but suffers from a lack of positive results. The present article reports several successful attempts to locate buried structures using the same equipment. As Darracott and Lake point out, the radar technique, like any geophysical approach, is limited by the natural conditions of the site and it is only by careful consideration of the geological and geophysical properties that the uncertainties can be reduced.

The present state-of-the-art of ground radar is such that useful data can be obtained from sites that are essentially free from a clay topsoil or otherwise relatively high conducting surface layer, as under such conditions radar penetration is limited to a few feet. Although it is true to say that much of the UK has a predominately clay topsoil there are nevertheless a great many places that are susceptible to radar penetration and clearly a multitude of other civil engineering applications exist for its use. Darracott and Lake state the factors that affect the use of ground radar and it can be seen, from the number of variables involved, that it is very difficult to theoretically predict its effectiveness at any one site.

As ground radar data accumulates this problem will become less but at present provisional test work, at individual sites, will remain the most costeffective approach. As with other geophysical methods, the more that is known about the physical properties of the site and its geology, the less is the uncertainty of data interpretation, Geological control is usually provided by borehole information or test pitting and without this knowledge only assumptions can be made as to the depth and character of the radar target. 

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