Report: APP CMHS Project 1

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3.6.4. Strata Control

Current Technologies

Typical mine strata control management process in the U.S. underground coal mines includes the following major components:

  • detailed site-specific geological and geotechnical characterisation using standard strata classification systems such as Rock Mass Rating (RMR) and Coal Mine Roof Rating (CMRR);

  • geotechnical assessment and numerical modelling

  • design of mine layout and mining sequence

  • design of strata support and reinforcement systems

  • strata control performance monitoring.

Various strata control technologies including both software and hardware have been developed and applied in U.S. to support the mine strata management. Key examples of the technologies are as follows:

  • The Coal Mine Roof Rating (CMRR) has been developed by US Bureau of Mines to quantify the defects in the rock mass and compile a strength value which can be used for engineering design. The CMRR has been applied to a number of ground stability problems, including chain pillar design, roof bolt selection, hazard assessment, intersection design, and numerical modeling.

  • monitoring devices such as wire extensometers and sonic probe extensometers;

  • high strength rockbolts and cable bolts.

Application Sites

Effective strata control is critical for underground coal mines and therefore has universal application, though the potential solutions will vary dependent upon conditions.

Technology Gaps/Needs

There are highly sophisticated numerical techniques for modelling variously shaped openings in discontinuous and heterogeneous materials. However, simplifications are almost always required to reduce the problem to a manageable level. A fresh look needs to be taken to model in situ conditions more accurately.

There is a need to investigate the applicability of current or newly developed technology in detecting voids, especially those containing water, and should consider the benefits of developing routine procedures to improve mining in the vicinity of old mines and at-risk geologic conditions.

At great depths, violent failures of pillars and longwall faces produce extreme hazards to underground workers and contribute to mining-induced seismicity. The potential for bursting could be reduced by appropriate mine layout and mining sequencing. Research into the relative merits of various mine design scenarios would likely reduce hazards and optimise resource recovery.

There are ongoing needs for technological improvements in the following areas:

  • prediction and planning of strata control in multi, deep, thick seams;

  • continuous real time strata monitoring and data interpretation;

  • rapid and automated roof bolting, skin support materials and rapid placement method.

Current innovations and knowledge are broadly sufficient for the majority of mining conditions in U.S, although roof falls on longwall faces or gate roads continue to be the major safety concern.

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