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The biggest risk to operations in Polish copper is high-energy seismic tremors where hypocenters are located within the main roof strata. These phenomena occur often in the areas which are virtually free of tectonic disturbances. They are extremely difficult to both predict and analyze due to their short duration and unpredictable time of occurrence. The objective of the presented analysis was to determine the overall stress/deformation states within the considered mining panel prior to the selected archival seismic event and afterwards to judge how the progress of mining could affect the occurrence of instability in the roof strata rock mass. Geomechanical problem solution and results visualization were based on the NEi-NASTRAN computer program code utilizing FEM in three dimensions.

Based on the finite element method formulated in three dimensions, a selected area of the salt mine has been modeled, embracing totally 2 separated, historically valuable mine rooms. The results of the computer simulations permitted elastic-viscous rock mass stability analyses identifying the areas being more susceptible to damage, presently and in a far future. The geomechanical risk assessment procedure utilized so called safety margins which were defined as a distance between the point characterized by the actual local strain/stress conditions and the instability (limit) surface(s) which location in the 3D stress/strain space could be determined using the well-known strength theories

Antropogenic seismicity is one of the most important geomechanical hazard encountered in Polish deep copper mines. Obviously, it may have a negative impact on the peoples safety and the production process. In such circumstances, a number of both active and passive prevention measures have been implemented in the mines, at least partially. One of the most effective, applied for many years, active means used for seismic hazard reduction, is multi-faces blasting works which by assumption should result in release of strain energy accumulated in the rock mass by inducing seismic events in the areas of high strain concentrations. However, at the stage of blasting works design process, a most of attention is paid rather on the vibration amplitude increasing than on the effect of its frequencies. In result, one of the basic parameters of induced seismic waves, which is the frequency of vibrations is usually omitted. Nowadays, the frequency of the seismic wave initiated by firing of group of faces is basically out of control due to the low accuracy of detonators utilized today. Taking the above into account, the possibility of increasing the effectiveness of blasting provocation by controlling the frequency of induced seismic waves was analysed as the effect of the frequencies values assumed to be the dominating ones, around which the computer based 3D FEM solutions of the blasting operation has been simulated.

The exploitation of copper ore deposits in Polish underground mines is performed primarily by the use of blasting technology which seems to be relatively well suited to the hardness of the local rocks and to local mining and geological conditions. Blasting works are also recognized as an active method of seismic events prevention, conducted as group strain-release blasting within potentially instable main roof strata and in pillars. A notable number of recorded dynamic events can be clearly explained by the blasting works effects. However, these operations are presently conducted intuitively based on a trial-and-errors basis, rather than upon an intentional and scientifically justified approach. As a one of seismic hazard reduction measures, a special kind of group winning blasting conducted with appropriately selected delays between the successive face-detonations is presented in the paper. This approach is able to amplify purposely the energy of rock mass vibration within the area which has been identified by the FEM modeling as a potentially instable. As a result of the entire multi-faces blasting operation one may expect the rock mass possibly distressing manifested as a seismic event. The presented analyses have been supported by a 3D FEM dynamic modelling of multi-face blasting in different configurations of space and time coordinates.

Extraction of the copper ore deposit in the Legnica-Glogow Copper Basin in Poland is usually associated with high seismic activity. In order to face this threats, a number of organizational and technical prevention methods are utilized, from which blasting works seem to be the most effective. A significant number of recorded dynamic events may be clearly and directly explained by the effects of this approach. It is also expected, that the simultaneous firing of a number of mining faces may provide the amplification of vibrations in a specific location chosen within the rock mass. For better recognition of a such process, formation of an elastic wave generated by the detonation of explosives in a single mining face have been evaluated using the numerical tools and verified by the field measurements of ground particle velocity and acceleration parameters, i.e. PPV and PPA parameters. The primary objective of presented paper was to find the bridge between numerical simulations of the time-dependent seismic particle velocity values induced by blasting and in situ measurements using seismic three component geophones

One of the major problems associated with exploitation of the copper ore deposit in underground mines in Poland is the local disturbance in a state of stable equilibrium manifested in a sudden release of strain energy stored in the deformed rock mass. It occurs mainly in the form of dynamic events which may result in rockbursts and roof falls. In order to face this threats, a number of organisational and technical prevention methods are applied in mines. It should be also noted that the greatest difficulties with the roof control are observed in the vicinity of active mining fronts, where the highest deformations are observed. The detonation of explosives generates a propagating shock wave which may cause a serious damage to a material body that is encountered on its way. Thus, a number of doubts during the mining operation emerged, that simultaneous firing of group of mining faces may have the negative impact on the condition of applied roof support and condition of roof strata as well The article discusses geomechanical influence of multi-faces blasting on immediate roof strata condition through the mutual comparison of the instrumented bolts monitoring data and the computer simulations results. The numerically assessed stress/strain field in the near vicinity of the blasting works operation has proved to be in close agreement with the field measured data. In the considered mining conditions both the numerical approach and field strain/stress monitoring indicated the low effect of production blasting on the immediate roof fall potential.