Abstract
A prototype sonde has been developed to establish whether distance and, hence, movement can be measured over short ranges by the use of low-frequency electromagnetic fields. An initial trial under laboratory conditions demonstrated that the principle could be used for measurements through air, though the measurements were affected by temperature and by vehicle movements outside the laboratory. Subsequent field trials at an abandoned mine produced measurements through up to 20 m of rock that were very close to the surveyed distances. Finally, a two-week trial of settlement monitoring undertaken in a roadway in the harsh underground environment of Boulby salt and potash mine confirmed the potential of the technique for accurate measurement of convergence and separation. Further tests of the ability of the sonde to measure settlement through fill are now planned.
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