Application of PPV method for the assessment of stability hazard of underground excavations subjected to rock mass tremors

Longwall 3/503 in the Bobrek-Centrum mine was extracted in the period from May 2009 to July 2010 and was characterized by a very high level of seismic activity as well as high energies of mining seismic tremors. The rst period of the increased seismic activity accompanied longwall start-up and was connected with the vicinity of residual area capable to accumulate energy and generate strong seismic events up tu energy 107 J (Figure 1). Another increase of seismic activity was registered when face line of longwall 3 in seam 503 was gradually coming out of the mined area of seams 509 and 510 (October 2009 to February 2010). During the time longwall 3 exploitation was being carried out there were also strong tremors not only directly connected with mining, but also those, which were of a regional character and where mining was a trigger factor of low magnitude seismic events. These seismic events took place during the period when face line of longwall No 3 was approaching the bottom of Bytom Syncline. The strongest tremor of regional character during mining of longwall panel No 3/503, occurred on 16.12.2009 and was of seismic energy of 8·108 J (local magnitude M = 3.5). Figure 1 presents distribution of seismic energy during mining of longwall panel No 3/503, i.e. in the period from 2009.06.01 to 2010.07.01. After such a strong tremor took place, there was a problem with the assessment of hazard stability of mine excavations of longwall 3/503. In January 2010, geophone probes were installed with the aim of assessing the level of peak amplitudes of vibration velocity (PPV) occurring in side walls of longwall excavations as the result of the in uence of strong tremors of rock mass. The rst seismologic analyses of strong tremors of regional character indicated a considerable depth of their foci of tremors, even up to several hundred meters