Borehole measurement of the E.M. properties of sandstone

Some cities are built on massive sandstone deposits and for the addition of services or infrastructure such as railways, road expressways and sewers, tunnelling through the sandstone may be an attractive alternative to the acquisition of land and buildings for surface construction. Whilst the overall route of a long tunnel would be carefully surveyed at intervals using available geophysical techniques, smaller scale sensing of material properties ahead of a tunnel-boring-machine may be desirable to avoid problems and delays. Looking ahead of the machine with a probe measuring complex dielectric constant may provide one means of remotely sensing changes in sandstone properties. The dielectric properties of sandstone are measured in a test borehole which passes through a “soft” region and compared with the properties measured in adjacent “hard” regions