This case study illustrates longer term, tactical monitoring for a dataset over the period of four and a half months. The country rock for which this dataset was collected is situated in a basalt, a hard, brittle rock mass that is defined by structurally opposed to rock mass instability. The instabilities tend to form with very little deformational warning.
The schematic diagram illustrates a relative range synthetic map set at a 30 mm scale, the relative range, average velocity, velocity delta and the temperature and refractivity plots for a region of the basalt. For a period of four and a half months, a scale of 30 mm on the relative range plot is a very small scale.
The trend lots illustrate the average movement for this portion of the pit slope, which is a 30 000 m2 area, a user defined area (50 m2) and a single point. One may assess the overall stability of an area as well as predetermined zones (where prisms or other sensors may be available) as well as areas that may be demonstrating developing movement.
With longer term datasets, discrete interrogation of the collected data for different periods of time can be conducted. The relative range, average velocity and velocity delta synthetic maps may be assessed by selecting an ascending scale (mm or mm/hr) and then time windows in order to identify an area of developing movement. Typically, for brittle rock masses, a shorter time window is employed in order to sensitise the trend plots to the selected alarm limits. The reference and end time may also be selected in collaboration with the various time windows in order to represent movement patterns identified on the synthetic map. In some cases, there may be periods of activation and deactivation dependent on the mode of instability, mining activities or trigger events that initiate periods of activity. Notes pertaining to these events can be added to the trend plots in order to maintain a history for the slope. This case study provide an example for reference purposes.
This type of database assessment method is especially useful for the calibration of alarm levels and the trigger action response plan (TARP) if empirical, back-analysis and comparative methods where used for the compilation of the TARP procedures.
The refractivity plot shows a total variance of approximately 60 ppm over the period of the dataset, with little variance between individual scans. Considering the weather patterns at the time of year when the dataset was collected which was the rainy season, there was negligible effect on the movement trends as illustrated trend plots.
