What’s New AUTOMATED SURVEYING

Geodimeter of Canada has fully automated the monitoring of walls in open-pit mines. The company’s total station survey system, the AGA 710, which is used for monitoring the structural stability of pit walls at many Canadian mines, can now collect data all day and night without the need of a surveyor. The first installation of the new, smaller and lighter instruments, the 140 SMS, is in an open-pit mine in eastern Canada — at Quebec Cartier Mining’s big iron ore mine in Fermont, Que., near Labrador.

Since 1974, Geodimeter’s popular AGA 710 has replaced labor-intensive monitoring methods using borehole extensometers and theodolites in most open-pit mines in British Columbia, Alberta and Saskatchewan, according to Dr Garston Blackwell of Geodimeter. Short holes, two inches deep and 1/4- to 3/8/-inch in diameter, are drilled into the rock to be monitored; a sho rt steel rod with a reflective prism on top and a small overhanging protective covering is inserted in the hole and secured. Light from the survey instrument reflects off the prism and returns to the instrument. By measuring the travel time of the light, the instrument calculates the distance to the prism.

In the mid-1970s, Geodimeter introduced a punch tape unit to collect all the data from the instrument, thus minimizing human errors. The most recent advance has been the development of the Geodimeter 140 SMS, a motorized survey instrument which can turn angles automatically. The unit is controlled by a micro- processor and is equipped with a miniature electronic memory. The instrument receives instructions from a micro-computer and communicates with the instrument to turn vertical and horizontal angles and measure both angles and distance to the reflecting target.

The instrument is instructed to point to the last location of a particular target and search for a suitably strong reflection. By maximizing the signal strength of the reflected light, the target is relocated and the new location communicated back to the micro-computer. Continued excessive movement over a monitoring period of weeks or days causes the micro- computer to issue a warning that a rock-fall is possible.

A computer-aided design system (AUTOCAD) is being used to show the movement history of a prism and to plot target locations in three dimensions, Blackwell says. The direction of movement for any group of reflectors can be shown from any position and any recorded instability can then be investigated quickly and effectively. The only drawback is the inability to know what displacements are taking place deep in the rock wall.

Many of the fundamentals of pit- slope-monitoring were developed in 1978 at the Brenda mine in British Columbia. Using the Geodimeter system, Brenda Mines was able to properly design blasts and predict how much water should be pumped from an unstable wall of the mine to avoid failure. This allowed the company to mine about 50,000 tons of high-grade ore before the wall failed.