Underground » Coal Burst
Stress state and geotechnical conditions often change significantly near major geological structures which is the cause of most major mine instabilities and/or safety hazards including coal burst, roof falls, water inrush, gas outburst etc. This project aimed to develop an integrated method of mapping the stress state and strain energy during mining near the major geological structures. After knowing the strain energy and the related stress state, the risk of coal burst in a roadway can then be quantified for risk control purposes.
The research work included:
- A comprehensive field monitoring program in the vicinity of a major geological structure in a selected mine site;
- Detailed analysis of monitoring data to identify the stress anomalies near the geological structure and evaluate the possibility of using the monitoring tools for coal burst forecasting;
- Three-dimensional numerical modelling to investigate the stress distribution and the strain energy concentrations for the purpose of risk mapping of coal burst.
For the integrated field monitoring, Mine A was selected as the monitoring site where pressure bumps The key results from the field monitoring were:
- Stress regime;
- Monitoring system sensitivity;
- Pressure bump monitoring;
- Effect of dyke;
- Strain energy distribution;
- Stress distribution near reverse faults; and
- Risk of coal burst.
In summary, this project provided a quantified field evidence that the stress concentration occurs near major geological structures. This stress concentration could lead to high strain energy concentration in the rib of a roadway, and hence increase the risk of coal burst.
The mechanisms that a dyke or a reverse fault influences the stress regime can be very different. Based on the field monitoring and/or numerical investigation in this project, high stress concentration tends to form in the “hanging wall” of a dyke but in the “footwall” of a reverse faults.
Both microseismic and stress monitoring are highly sensitive to capture fracturing events at a distance, and hence have the potential to be used for coal burst and outburst forecasting. However, due to the complexity of sudden dynamic failures, these monitoring systems have limited success in detecting the precursors (if any) of pressure bumps and hence may not be suitable for coal burst prediction yet. For microseismic monitoring using the current configurations, the limited accuracy of event location (±5m) made it difficult to map the detailed strain energy density distribution in a roadway rib. New microseismic sensors using fibre optics could overcome this shortcoming. Numerical modelling should be used to assist quantifying the strain energy and the risk of coal burst.