The use of high-definition magnetics in engineering site investigation

Abstract

Recent advances in magnetometer technology have resulted in high-definition magnetic mapping becoming a rapid and effective aid to engineering site investigation. Conventional magnetometer systems were usually too slow to be economical for mapping magnetic fields in the detail required to resolve near-surface geological and cultural structures of importance to the engineer. A new, self-contained magnetic exploration system, capable of measuring and image processing on location up to 100 000 measurements per day, is now being used in many engineering applications. Measurement densities of up to four per square metre are necessary to define the Earth's magnetic field comprehensively in a plane half a metre above the ground surface. The instrumentation described is capable of economically acquiring and processing these data at up to two hectares per day. Geological and cultural features that may be detected and mapped using magnetics, and which are relevant to engineering site investigation, are intrusive dykes, sills and pipes, geological faults and contacts, unexploded ordnance, ferrous industrial waste and utilities, and buried archaeological artifacts. The technique has been effectively applied to engineering problems relating to mine planning, excavation site analysis, ground-water flow control, explosive ordnance detection, industrial waste relocation and archaeological site investigations.