Syncrude Research, with the support of AOSTRA is currently examining three technologies as potential candidates to replace the existing slope inclinometer system which is used extensively in the Mine and Tailings areas to monitor ground movement. The technologies are coaxial cable, optical fibre, and electrolytic bubble sensors, each of which has the potential to provide continuous remote readings at an acceptable cost. Most important, these technologies hold the promise of a safer, more efficient dragline mining operation as a result of reduced downtime and better understanding of highwall movement.
The slope inclinometer system currently used to monitor highwall slope movement is described together with opportunities for improvement with a new system. The technologies of coaxial cable, optical fibre, and electrolytic bubbles are being evaluated. The basic principles of operation of each system are presented together with preliminary laboratory and field test results.
Syncrude Canada operates an oil sand mine in northern Alberta producing 57M barrels of synthetic crude oil in 1990. The oil sand is mined by large draglines which operate adjacent to the edge of the highwall which varies in depth from 40 to 60 m. A number of factors such as stress relief, high pore pressures and adversely dipping clay beds contribute to instability or highwall movement during and after the mining process (Fair & Lord 1984, Holmes & List 1989).
An extensive highwall monitoring program including slope inclinometers contributes towards a safe and efficient mining operation (Fair & Isaac 1985). However, Syncrude with the support of AOSTRA, is investigating new technological opportunities which potentially offer improved highwall monitoring techniques.
Slope inclinometers form a key component of Syncr Ude's current highwall monitoring program and in 1990 850 were installed. A vertical hole 120 mm in diameter and 25 m deep, is drilled in the highwall bench at locations prone to movements. ABS plastic casing, 59 mm diameter with longitudinal grooves at 90 degree intervals, is placed in the borehole and grouted into place A travelling inclinometer sensor or probe which consists of a biaxial servoaccelerometer is lowered to the bottom of the casing. The sensor is centred and guided by two sets of spring loaded wheels 600 mm apart which ride in the grooves of the casing. A voltage output monitored by the readout unit at the top of the hole, is proportional to the inclination of the servoaccelerometer. The inclinometer sensor is then raised in 600 mm (2 It) increments to measure the inclination of the casing as a function of borehole depth (Figure 1) (Dunnicliffe 1988). Readings are repeated to produce subsequent casing profiles from which the displacement of the casing from the initial position is calculated. This value is assumed to be equal to the ground movement in the highwall.
The position and spacing of slope inclinometers is determined by the Highwall Engineer alter considering the highwall geology and the experience gained while mining the area previously (Figure 2).