ABSTRACT
Judicious placement of extensometers within stope blocks provided early information on the response of the rock mass to stoping at the Porgera Underground Gold Mine in Papua New Guinea. The results of the programme, carried out during the first years of production, formed the basis for optimization of ground support and reinforcement usage.
The instruments used were rod extensometers incorporating seven equidistant anchors, ranging in length from 21m to 25m. Each instrument was fully grouted in a 102mm diameter percussion borehole, and read daily using a dial gauge.
The choice of rod extensometers was made on the basis of ease of use, cost and reliability. They also have the advantage of providing a lot of readily interpreted data without the complication of a lot of mathematical analysis, which in a new operation with little back-up in absolute numbers, would have proved onerous. The instruments were well suited to the application of monitoring a complex blocky rock mass in a low stress environment, where the location and nature of individual structures was not well known, and a knowledge of relative displacement within the rock mass was deemed to be critical. A selection of examples have been chosen to highlight the adaptability of the instruments in achieving this goal.
