Mining

The IMS seismic system is designed primarily for use in the mining environment.

The seismic system is tailored to meet the specific monitoring requirements and objectives of any mining operation.

Applications

  • deep-level hard rock gold and platinum mines
  • coal mines
  • base-metal mines
  • kimberlite (diamond) mines

Mining Environments

IMS systems have been installed in many different mining environments with a wide range of mining methods, including:

  • narrow-reef tabular longwall, sequential grid and scattered hard rock mining
  • longwall and bord-and-pillar in coal mines
  • block caving and sub-level caving
  • underground open stoping
  • longhole stoping
  • open cast mines

UNDERGROUND HARD ROCK

Operation

Real-time seismic monitoring of the rock mass occurs via a permanent underground installation of seismometers (consisting of a combination of seismic sensors and data acquisition units), which communicates with the central computer located on surface. A GPS timing module is used so that recorded seismic data may be integrated with seismic data from other nearby seismic systems for sharing of information about regional seismic events.

Communications

Multiple netADC units are linked to a seismic processor via Ethernet cable. The seismic processor communicates via DSL protocol with the central computer on surface. This is a cost-effective approach, as it uses inexpensive 2-core twisted-pair copper cable to communicate over long distances with high data rates.

Alternatively, if fibre optic lines have been installed and a reliable link to surface is possible, netADCs can be linked directly to the central computer for continuous streaming of Waveforms over Ethernet.

Any number of seismometers can be supported by an IMS seismic network.

Seismic Sensors

Typically our sensors are permanently installed into boreholes. This ensures the best signal quality, as the sensors are outside the fracture zone surrounding a tunnel. Certain temporary applications may allow for the use of removable borehole geophones.

A netADC data acquisition unit can monitor up to eight seismic signals, in any combination of uni-, bi- or tri-axial seismic sensors. Seismic processors can be customised to handle any number of netADCs. This means 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 and Interpretation

The seismograms of every seismic event that triggers multiple stations are transmitted 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. This data is then confirmed by manual processing with Trace. Spatial, temporal and source-parameter trends may then be detected and analysed using the Vantage interpretation package.

UNDERGROUND COAL MINING

Operation

Real-time seismic monitoring of the rock mass occurs via an installation of permanent surface and temporary underground seismometers, which communicates with a central seismic server located on surface. The integrated GPS timing module is used so that recorded seismic data may be integrated with seismic data from another nearby system for information about regional seismic events. Seismic stations on the surface use GPS modules to ensure common time with the seismic server and, therefore, the underground seismic network. The GSi units are intrinsically safe and can be used in the potentially explosive underground environment. These units use a 2-pair cable for communication and power from a safe area.

Communications

Digital radios are used for communication between surface seismic stations and the central site. From the mining offices or a safe area underground, two twisted-pair copper cables pass through standard intrinsic safety barriers to service the underground GSi stations. Up to three GSi stations may use the same communication and power cables, provided these cables are not longer than 2 400 m. Alternatively, a single GSi may use two twisted-pairs, provided this cable is shorter than 7 000 m.

Power

The low power consumption of the surface seismic stations (less than 0,6W/channel) allows for the use of an inexpensive solar-panel-and-battery unit. The solar power, together with digital radio communications, means the seismic station may be located in areas that cannot be linked to the central seismic server by fibre-optic or copper cables. The underground GSi stations use less than 120 mW each, and are supplied with power from the central server or fresh-air zone.

Seismic Sensors

Surface stations typically use geophones installed temporarily in shallow holes or permanently into boreholes for the best signal quality. Underground, the fast pace of mining makes this approach expensive, so sensors mounted to the tunnel surface are commonly used. These surface-mount sensors can quickly be moved to keep up with mining.

Each netADC can monitor and pre-process up to eight seismic signals, in any combination of uni-, bi- or tri-axial seismic sensors. Geophones and accelerometers (piezoelectric and force-balance) are currently supported, although geophones are more commonly used in the low-stress-drop environment of most coal mines. The GSi units monitor up to three seismic signals from a single tri-axial geophone or three uni-axial geophones. The geophones have been certified as intrinsically safe.

Seismic Data Processing and Interpretation

The seismograms of every seismic event that triggers multiple stations are transmitted to the seismic controller, and recorded on a user-specific computer on the Local Area Network (LAN). 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. This data is then confirmed by manual processing with Trace. Spatial, temporal and source-parameter trends may then be detected and analysed using the Vantage interpretation package.

If preferred, seismic data can be processed off-site by IMS, and the processed data uploaded back to the mine. The target turnaround time for this process is five minutes. IMS also offers routine analysis and reporting services.

HARD ROCK OPEN-PIT MINES

Operation

Modern microseismic arrays are installed behind specific slopes in long inclined holes. The holes are drilled either 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 three-dimensional spread of seismic sensors around the volume of rock 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. The station either communicates with the central computer via digital radios, or seismic data can be recorded to a portable USB drive, using StandAlone mode. Seismic processors and netADCs are linked to GPS modules to provide accurate time synchronisation.

Communications

Off-line / StandAlone

In a StandAlone setup, seismic data is recorded to portable USB drives connected to each data acquisition unit. The USB drives are routinely collected, and the seismic data downloaded to a computer running Trace. Seismograms of common events are post-associated for off-line processing and interpretation. StandAlone operating is the most cost-effective form of communication for applications where real-time monitoring is not essential.

On – Line

WiFi digital radio and repeaters, or cellular modems, can be used to permanently connect the seismometers to the central site.

Power

The low power consumption of the seismometer (less than 0,6W/channel) and digital radio allows for the use of an inexpensive solar-panel-and-battery unit, rendering the seismic station completely independent.

Seismic Sensors

Each netADC data acquisition unit can monitor up to eight seismic signals, in any combination of uni-, bi- or tri-axial seismic sensors. Seismic processors can be customised to handle a scaling number of netADCs. This means 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 and Interpretation

The seismograms of every seismic event that triggers multiple stations are transmitted 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. This seismic data is regularly transferred to IMS’s offices for processing and quality control according to strict procedures. The data is then analysed, and a standard report and Vantage project regularly submitted to the mine geotechnical engineer. This way, all seismological tasks are accomplished off-site, with plain-English reports and data made available to the mine staff for interpretation.

CAVING MINES

Operation

Real-time seismic monitoring of the rock mass occurs via a permanent surface-and-underground installation of seismometers (consisting of a combination of seismic sensors and data acquisition units), which communicates with the central computer located on surface. The integrated GPS timing module is used so that recorded seismic data may be integrated with seismic data from another nearby system for information about regional seismic events. Data acquisition units on the surface use internal GPS modules to ensure common time with the central computer and, therefore, the underground seismic network.

Active seismic sources are used to create controlled sources of seismic radiation, which is continuously recorded by the passive microseismic monitoring array. As the cave grows, the rays are perturbed, and thus extremely accurate measurement of the seismic-ray travel times allows the cave growth to be tracked in near real-time — even in soft rocks, such as kimberlite, or low-stress environments, such as close to surface.

Communications

Multiple netADC units are linked to a seismic processor via Ethernet cable. The seismic processor communicates via DSL protocol with the central computer on surface. This is a cost-effective approach, as it uses inexpensive 2-core twisted-pair copper cable to communicate over long distances with high data rates.

Seismometers on surface can be linked to the central computer via cell modem or digital radio communications, which is cost effective and more practical than laying direct cable links.

Any number of seismometers can be supported by an IMS seismic network.

Seismic Sensors

The seismic array is carefully designed to monitor the cave initiation and propagation. Sometimes sacrificial sensors are installed ahead of the cave to better monitor the initiation phase. Usually, long holes are required to attain the three-dimensional coverage, which is vital for accurate seismic event locations. The IMS smart sensors detect their roll inside an inclined borehole. Therefore, the sensor orientation is measured even for long borehole installations. This information can improve location accuracy, and is essential for any advanced work on source mechanisms.

Each netADC data acquisition unit can monitor up to eight seismic signals, in any combination of uni-, bi- or tri-axial seismic sensors. Seismic processors can be customised to handle a scaling number of netADCs. This means that a single seismic processor can monitor and process seismic channels from multiple netADCs. Geophones and accelerometers (piezoelectric and force-balance) are currently supported.

Active Seismic Sources

Surface-mounted impact hammers are used to generate repeatable seismic energy at locations, such that the resulting rays will travel over the future cave to be recorded by the seismic sensors. While the energy is low enough for normal passive monitoring to be not disturbed, stacking many shots allows for the accurate measurement of velocity variations in near real-time — down to a resolution of 0,01% or better — over distances of up to 1 km.

Seismic Data Processing and Interpretation

The seismograms of every seismic event that triggers multiple stations are transmitted 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. This data is then confirmed by manual processing with Trace. This work is often completed off-site using IMS’s routine services. 3D ray-tracing can be used to improve seismic event locations, assuming some model of the geological and cave geometry. Spatial, temporal and source-parameter trends may then be detected and analysed using the Vantage interpretation package. A routine analysis and report is often performed by IMS. In particular, analyses of calculated source parameter histories provide information on cave ceiling advancement and changing stress fields as the cave front nears the surface.