Creating a Precise, Reliable, and Fully Automatic Real Time Monitoring System for Steep Embankments
The stability of steep embankments is a major safety issue in open pit mining, highway passes, and earth filled dams. A failure in any one of these situations could mean a loss of very expensive equipment, a long term inconvenience, and more importantly, a loss of life. These possible catastrophes could be avoided by installing a reliable real time monitoring system. Robotic total stations (RTS) give one possible cost effective solution to creating a near real time monitoring system. An RTS uses automatic target recognition (ATR) and servo motors to automatically point to each of an array of retro reflectors established within the area of concern. The observing sequence (cycle) can be scheduled to be repeated and compared to a base cycle to determine the slope stability without any human intervention. Warnings can be automatically generated if slope movements exceed a preset tolerance level.
Although it is better to err on the side of caution, false alarms can cut into production, profits, and unnecessarily cause concern. There are a number of systematic errors that are inherent in these kinds of observations that can diminish a system’s reliability. The systematic error caused by the bending of light rays in the atmosphere is a primary deterrent to creating a reliable system. In addition, instabilities in the instrument set up or in the reference targets used to create the datum can cause biases in the displacement patterns. Together these can create offsets in the displacement patterns that can be interpreted as apparent instabilities, which in turn create false alarms.
A methodology has been developed at the Canadian Centre for Geodetic Engineering (CCGE) for reducing the refraction and datum biases. The combination of raw observation differences and cycle averaging can minimize the refraction offsets. An iterative datum independent transformation can identify and remove the effects of unstable reference targets or instrument set ups. The methodology has been realized in the creation of a software package that has been installed successfully at a large earthen dam facility in California and an open pit mine operation in British Columbia.