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The challenge

Managing complex goaf

The goaf is a mining term which refers to the part of the mine from which the mineral has been partially or completely removed

Understanding the goaf-hole shearing process is vital in designing and operating an efficient goaf-gas drainage system, especially as goaf-hole failure is one of the critical problems in many gassy mine sites.

In coal mining theses challenges include:

  • complex goaf-hole shearing mechanism
  • methane gas drainage goaf-holes in longwall mining operate through various strata
  • mine-scale monitoring and experiments for investigating the goaf-hole shearing process is a challenging task
  • 2D modelling may provide only a partial answer and on occasion may provide erroneous answers to this truly 3D problem, and
  • developing and conducting a large mine-scale 3D modelling is complex and difficult.

Our response

Application of advanced 3D numerical method

We studied mechanical shear failure of goaf-gas drainage holes in an underground coal mine to evaluate the transverse, longitudinal and total shear magnitudes that were developed during longwall coal extraction.

We used an advanced 3D numerical method to study the goaf-gas drainage hole shearing mechanism in one of the Australian longwall mines.

We used our in-house advanced numerical tool to tackle this 3D problem with the real mine site parameters, using data on mining depth, width, height, length, geology and lithology.

This integrated approach allowed us to calibrate and validate the model parameters by combining the mine site monitored and observed data.

The results

Improved understanding of goaf-hole shearing mechanism

Using our advanced 3D numerical simulation, we were able to predict the magnitudes of both the longitudinal and transverse shears as well as total goaf-hole shears along the entire goaf-gas drainage hole length.

The study provided a unique understanding of goaf-drainage hole shearing mechanisms that were not possible to be investigated by 2D models.

The generalised conceptual goaf-hole shearing mechanism - the first of its kind - showed how goaf-gas drainage holes shear during longwall advancement.

The typical “signatures” of longitudinal and transverse shears and their influence on total shear along the goaf-hole can now be understood.

It has also been demonstrated that the maximum shear follows the angle of break.

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