Longwall coal mining relies on fracturing and caving of rock strata over the mined coal for safe and efficient operations. The fractures created lead to increased permeability, which may in turn impact surface and groundwater. Accurate predictions of these impacts are critical for environmental assessments of mines.
Predicting a complex system
In order for mining operators to confirm their social licence to operate, they must assess how their mine could affect the environment, and try to predict negative impacts in order to avoid them.
Their Environmental Impact Statement (EIS) must address all of these issues.
This is a particularly complex task when it involves underground ecosystems.
Potential issues include unintended disruption of surface and groundwater systems and mining-induced subsurface deformation, fracturing, surface subsidence and aquifer interference.
The extent to which this happens is largely controlled by local rock-strata conditions, mining methods and mine layouts.
Tools to predict from every angle
Knowing the potential for negative environmental consequences from rock fractures created during longwall mining, it is imperative to develop methods and tools that can properly consider all influencing factors, unlike traditional, empirically based methods.
We have developed unique modelling approaches, technologies and knowledge to accurately predict the extent of rock fracturing that will be induced by the mining process.
This capability assists in the assessment of mining impacts on water bodies and accurately predicts strata deformation and subsequent fracturing (particularly connective fracturing and subsequent permeability changes) in varied hydrogeologic environments.
This helps to assess the mine water inflow and impact of mining on groundwater and gas emissions
The tools and methods we’ve developed and research efforts include:
- advanced simulation of rock fracturing using implicit and explicit fracture mechanics codes
- accurate prediction of the height of connective fracturing induced by longwall mining
- a methodology for simulating fracturing associated with longwall coal mining, which is extensively documented for which all the source code is available
- a toolset of software programs to estimate aperture and connectivity
- a novel method for predicting connective fracturing accounting for site-specific geological and geotechnical properties of the rock mass and specific mining parameter.
Deeper knowledge for better environmental protection
Over past 15 years, through series of research projects funded by CSIRO and the Australian Coal Industry’s Research Program (ACARP), we have developed tools and techniques that have enabled the accurate simulation of rock fracturing induced by longwall coal mining, as well as the estimation of aperture and connectivity of these fractures.
This unique capability considers local rock-strata conditions (strength, stiffness, natural jointing and bedding), and mine parameters including mining height and mine panel width.
This has enabled us to produce a unique fracture network and a mine-site specific permeability “ramp” function, now used as the fundamental input for further hydrogeological assessment of mine operations.
Several approaches for estimating mining-induced strata permeability have been developed and are described in research reports and published papers.
This same fracture network and permeability ramp function allows for the prediction of gas flow from gassy seams located in the influence zone of active mining panels, increasing the safety of mine operations.