A rock mass instability was identified on a portion of an inter-ramp slope at a large open pit mine. The distance between the radar and the pit slope was 1 600 m. In this case, the trend plots are illustrating progressive movement in the cracking and dislocation class, however, this portion of the pit slope has not yet collapsed.
There are distinctive transitional movement patterns which is illustrated by the single point data. Upon further investigation of a selection of single point data for this study, it was observed that the pit slope is moving in a progressive but inhomogeneous manner over the impending instability surface.
The synthetic map of the point data collected by the radar system shows the relative range measurements at a scale of 500 mm for a period of 9 days. This is a significant amount of movement when likened with published empirical case studies.
There are three identified areas of the instability, represented by movement trends on the schematic image of the instability data for the relative range, average velocity and velocity delta. The first trend encompasses the entire portion of the instability to illustrate the overall movement trend (100 m in width by 50 m in height in green), the second trend is an area threshold size to replicate the alarm triggers (20 m in width by 15 m in height, dark blue) and a single trend point defined by the user (light brown) to identify the maximum amount of movement taking place on that portion of pit slope.
The movement of this portion of the pit slope starts prior to the commencement of the illustrated database. The trend plots show average velocity and velocity delta values that remain somewhat constant for the length of the database, for both the special area and the area threshold area which is a reflection of the progressive movement captured by the relative range trend. The point data however does show much more variance, and is reflective of the more cyclical movement patterns on the pit slope which may be attributed to progressive and regressive stages, or potential more discrete stick slip movement if representative of large scale discontinuities. As mentioned, the surface of the instability is behaving in an inhomogeneous manner as the slope deforms prior to collapse.
Dependent on the trigger action response plan (TARP), once the relative range exceeds a certain value indicating the transition to the pre-collapse or collapse class of movement, the average velocity and velocity delta alarm settings, along with a shorter time window may be calculated and applied. This action may be completed in order to sensitise the alarm settings to more discrete movement trends in order to provide adequate warning for the response and planning phases of the TARP as required.
The temperature and reflectivity trend plots are illustrated for references purposes. This operation is located at a high altitude with clearly defined diurnal fluctuations of temperature, humidity and pressure. The refractivity plot is considered acceptable, however there is a slight effect on the trend plots illustrated until Day 5, thereafter the trends normalise.
