Rockburst is one of the most serious hazards which threaten the safety of mine operators and the underground and surface stability. Several geophysics and numerical approaches have been developed since the sixties to assess rockburst potential in underground hardrock mines. Some of the approaches are based on energy balance, Energy Release Rate (ERR) and critical energy and more recently the strain Energy Storage Rate (ESR). This paper presents the numerical results of a triaxial test of the critical energy, the critical energy depending on the confining pressure. The energy approach applied to a case study for the assessment of rockburst potential in a room-and-pillar copper mine in Poland was carried out. The Energy Storage Rate (ESR) is numerically calculated to predict burst occurrence.
Rockburst causes rocks to crush and collapse together. Several factors are known to have an impact on the rockburst hazard (Hudyma, 2004): depth of mining, geology and tectonics, thickness of orebody, geomechanical characteristics of rock-mass. Some of the mining factors also have an influence on the occurrence of rockburst: mining method, roof control method, pattern of deposit cut, concentration of mining operations, spatial limits of mining operations.
To improve the control of the mining induced seismicity a methodology for managing the seismic activities of the underground coalmines was developed, it combines numerical modeling; seismic monitoring, stress measurements and back analysis of sever rockburst cases (Fig. 1). The interaction between tools allows predicting seismicity and improving the surface installation and mine safety. The numerical modeling and seismic analysis are used together to help the prediction and the evaluation of rockbursts potential.
Another approach is the consideration of energy instead of stresses. Various methods involving energy balance have been developed. The evaluation of the Energy Storage Rate (ESR) provides an indication on the state of the rock surrounding an excavation.
This paper presents a numerical modeling using FLAC-3D software to calculate the ESR and critical energy. The efficiency of the modeling technique is demonstrated for a cylindrical excavation in an infinite elastic rockmass under hydrostatic stress. A method for the calculation of critical amount of energy stored in the particular case of a triaxial test is presented. The calculation of energy is then applied to a case study of a Polish underground mine, showing the need to define accurate levels of critical energy.