GPS navigation techniques in open pit deformation monitoring

Australian open pits are usually designed with steep slope walls to reduce the volume of waste material to be mined. However, steep slope walls are associated with a higher incidence of pit wall failure, posing safety and financial risks to mine operators. Therefore, deformation surveying has become an integral part of Australian open pit mining operations. The open pit environment is particularly harsh for GPS deformation surveying, due to restricted satellite visibility, severe multipath for sites situated on or close to pit walls and strict financial and safety constraints on the frequency of monitoring individual points. In these conditions, conventional rapid-surveying GPS techniques tend to be unable to reliably produce the centimetric-level accuracies necessary for detecting precursor movements to pit wall failure. This paper describes the methodology for GPS pit wall deformation monitoring developed at Curtin University, whereby small pit wall motions (<1 cm/day) are treated as in a very slowly moving navigation problem. Repeat rapid GPS surveys of 15 seconds interval provide data which are integrated with data observed from previous surveys. The integration of all available data can be achieved by using optimal Kalman filtering estimation techniques. The result is a robust system which can provide reliable deformation estimates in environments, such as open pits, where satellite visibility restriction can be severe. The process is illustrated with results from tests conducted in an open pit in Western Australian.