The influence of strata and tectonics on the rockburst risk in Polish mines

摘要

Mining induced events are not only a result of large depth of excavation but also lithologic structure of overlying rocks. In our experience so far, roof strata with high risk of large seismic events are generally characterized by two layers: the fractured, quasi-ductile layer just above a tabular cavity and the brittle, strong layer with rather larger thickness above the ductile layer. High risk is also associated with existing fault or weak zone. A qualitative model to account for these interactions is proposed. The model includes a few stages of process which appear prior to the occurrence of strong seismic events: splitting of the beds on lithological borders, bending fracture plane upward producing echelon zones and antithetic fractures that harden and soften rocks near the fracture zone. The bending of fracture plane that forms echelon zones and antithetic fractures is correlated with anomalous number of seismic events and their energy distribution. The special statistic procedures are shown which allow distinguishing this anomalous emission.