Slope stability radar (SSR) remotely scans rock slopes, continuously measures surface movement, and detects wall movement with sub-millimeter precision. The radar waves penetrate rain, dust, and smoke to give reliable measurements 24 hours a day.

This is a far cry from the crude measures we used in the early 1970s to monitor slope movement on the cut for the Daspoort tunnel in South Africa. We could see the tension crack at the top of the slope; so we put a rod in the ground on either side of the crack, tied a piece of string to the rod in the failure mass and put the other end over a pulley atop the second rod. We stationed an unskilled laborer at each such "measuring station" and gave him instructions to blow the whistle, sound the horn and whirl the whir-whir if he saw the string move over the pulley. The tunnel was built, the cut backfilled, and the cause of failure traced to water from the regular Saturday washing of the concrete trucks.

Drs. Harris, Noon and Rowley of the South African Institute of Mining and Metallurgy write of the use of SSR in their recent paper Case Studies of Slope Stability Radar in Open Cut MinesCase Studies of Slope Stability Radar in Open Cut Mines. They describe the use of SSR at the Mount Owen Coal Mine in the Hunter Valley, Australia. Apparently this is the deepest open cut mine in Australia with depths in excess of 270 m. SSR was used successfully to monitor slope failure and avoid incident. An observer of the failure described it thus: "There were few tell-tale signs when it failed, no rilling of material over the dump, no rapid opening of cracks, no dust, no noise, only minor trickling of material along the day-lighting surface of the surface" and "Strange silence prior to failureā€¦then I saw the ramp just raise 10m in the air at a rate of about one meter per secondā€¦."

The promise of SSR is set out thus by the authors: "SSR will contribute significantly to safety and mine design by providing accurate, reliable deformation data that may be later reviewed to further develop our understanding and analysis of failure mechanisms in open pit mine; eventually leading to improved slope design."