Developed by CSIRO, the "hi-tech canary", which has already been trialed at 15 underground coal mines in Queensland, New South Wales and China, sets alarm bells ringing at the first sign of danger.
"The technology, which operates remotely, will make mining safer and improve the way mines are designed in the future," CSIRO research group leader Mark Berry said.
"By enabling miners to deal quickly with hazards, the technology will save mining companies millions of dollars in lost production costs, with mines losing up to $1 million a day whenever work stops. This amounts to hundreds of millions of dollars every year in Australia alone.
"The technique, called microseismic analysis, centres on the fine measurement of seismic waves generated in rock under stress from mining."
The research team developed sophisticated instruments and data processing and visualisation tools for the analysis, which can be conducted remotely, up to 700 metres from the mining area.
Arrays of geophones, devices with a wire coil inside a magnetic field pick, up the seismic waves which cause the coil to move in the field, generating a voltage.
Signals from the geophones pass via cable to CSIRO's data acquisition system, where they are amplified and recorded.
"Different kinds of rock failure have different seismic radiation signatures, so geophysicists can differentiate between shear and tensile failure," CSIRO scientist Dr Xun Luo said.
"By comparing parameters, including amplitude and arrival times of P (fast, longitudinal) and S (slow transverse) waves, we can pinpoint the location and orientation of the fracture."
Microseismic monitoring also provides estimates of the size of the fracture and the energy of the seismic waves generated.
"At one site, an underground coal mine in central Queensland, engineers were concerned that mining would reactivate a fault through the coal seam, causing the mine's roof to collapse,” Luo said.
"We detected no significant seismicity in the fault zone. Daily reports of weak seismicity meant mining could proceed without interruptions that could have cost the company millions of dollars," says Dr Luo.
In another case, a NSW colliery faced the risk of fire from sudden, unpredictable methane gas emissions during mining. Microseismic monitoring by CSIRO correlated periodic, low frequency seismic waves with some emissions. The emissions lagged the seismic waves by three days.
In the future, microseismic analysis will enable miners to predict gaseous emissions and evacuate personnel if necessary.
Meanwhile, the theoretical knowledge gained from the project will put more geotechnical science into mine design, enabling engineers to come up with safer plans.
Industry collaborators on the microseismic monitoring project included the Australian Coal Association Research Program (ACARP), Southern Colliery, Moranbah North Mine, and South Blackwater, all in Queensland, and Dartbrook Mine in the Hunter Valley, NSW.
