Development of a highwall monitoring system using time domain reflectometry

Syncrude Canada Ltd. operates a surface oil sands mine in northern Alberta which produced 67 million barrels of high-quality, light sweet crude oil in 1993. The oil sand is mined by large draglines which operate adjacent to the edge of the highwall which varies in height from 40 to 60 m. A number of factors such as stress relief, high pore water pressures, and adversely-dipping clay beds contribute to instability or highwall movement during and after the mining process. To ensure safe, reliable, and economical mining, Syncrude has an intensive highwall monitoring program that includes 24 hour visual monitoring supplemented with geotechnical instrumentation. This paper discusses one component of the Syncrude Highwall Downhole Sensor Development Program in which field and laboratory studies were conducted cooperatively with the U. S. Bureau of Mines to investigate the use of time domain reflectometry (TDR) for highwall monitoring. Coaxial cables were grouted into boreholes and monitored using a TDR cable tester. While the technique shows great potential, it was not considered to be a suitable replacement for slope inclinometers given the stringent displacement monitoring requirements.