Development of a very low frequency magnetic sonde to measure distance through rock

The move towards room and pillar extraction methods with roof bolting for support has resulted in stopes and roadways needing to remain open for considerable periods. Monitoring of rock mass movements is important not only from a safety aspect but also from an economic standpoint. Rock mass behaviour is a valuable indicator of roadway life and allows accurate mine planning to be achieved. Manual data collection is expensive and often impractical. Automated methods are currently available in the form of single and multipoint extensometers, strain gauges, and stress meters. These systems require precise installation, are expensive and often have a limited range of measurement. Instrumentation of this type eventually becomes inaccessible and this can prove expensive. This paper discusses the development of a low cost alternative that can monitor rock mass movements over a range of 1-20m through rock and other solid material.