Hard Rock Open Pit Mining
Modern microseismic arrays are installed behind specific slopes in long inclined holes. The holes are either drilled from access points on the slope (ramps or berms) or, if necessary, from outside the pit. The design of the array should result in a 3-dimensional spread of seismic sensors around the volume of rock that is of interest.
Usually multiple sensors are installed into each hole. These sensors are connected to a data acquisition unit at the top of the hole. Station either communicates with the central computer via digital radios or alternatively, seismic data can be recorded to a portable USB drive, using StandAlone mode. Seismic processors and netADC’s are linked to GPS modules to provide accurate time synchronization.
- Off-line / StandAlone:
In a StandAlone setup, seismic data recorded to a portable USB drive, connected to each data acquisition unit. The USB disks are routinely collected and the seismic data then downloaded a computer with Trace software package. Seismograms of common events are post-associated for off-line processing and interpretation. This StandAlone operating is the cheapest form of communication for applications where real-time monitoring is not essential.
WiFi digital radio and repeaters or cellular modems can be used to permanently connect the seismometers to the central site.
The low power consumption of the seismometer (less than 0.6W/channel) and digital radio allows use of an inexpensive solar panel and battery unit, making the seismic station completely independent.
Each netADC data acquisition unit can monitor up to 8 seismic signals, in any combination of uni-, bi- or tri-axial seismic sensors. Seismic processors can be customized to handle a scaling number of netADCs, meaning that a single seismic processor can monitor and process seismic channels from multiple netADCs. Geophones and accelerometers (piezoelectric and Force-Balance) are currently supported.
SEISMIC DATA PROCESSING & INTERPRETATION
The seismograms of every seismic event that triggers multiple stations are downloaded to the central computer. The seismic event is automatically processed and seismic source parameters including the location, time, radiated seismic energy and co-seismic inelastic deformation are automatically calculated. The seismic data is regularly transferred to ISS’s offices. Here the seismic data is processed and quality controlled according to strict procedures. The seismic data is then analyzed and a standard report and Vantage. project regularly submitted to the mine geotechnical engineer. In this way all seismological tasks are accomplished off-site, with plain-English reports and data available for interpretation by the mine staff.