Materiały konferencyjne SEP 1992

460 Underground Exploitation School '92 actions result from smali seismic events that occur within the seam and are initiated by drilling and changes in th6 ambient stress field. Thus, it should be possłble to record these events and obJectively ąuantify and evaluate them. Figurę 3 shows such a record where, durłng i ncreasing ho 1 e depth, the background drilling noise is seen together with some events of higher amplitudę, Freąuency analyses of the drilling noise (figurę 4) and of events (figurę 5) show that the event signals have a main freąuency of about 700 to 800 Hz while the permanent drilling noise 1 ies in the rangę of 200 to 400 Hz. Thus, by fiItering band pass, t he s i gna1-to-noise ratio can be i mproved and indlvidual events can be recorded and evaluated more easily. On the basis of results such as these, a portable intrinsically safe device has been design, which allows on-line evaluation of the seismic signals or "seismic seam reactions" produced during testing or destressing operations. A błock- diagram of this device is shown in figurę 6. The signals are not recorded as a time-series. For every signal event two characte- ristic parameters are evaluated: the maximum amplitudę and a value corresponding to the energy content of the signal. These data, together with the time of occurrence of the event and some technical dri11ing data, are stored in a semiconductor memory. On surface, this memory is read out and the data are stored on a floppy disc for further evaluation. The data also are plotted in various forms. An example of such a plot is shown in Figurę 7, which summarizes the values recorded as the dri11ing proceeds. There appears to be a good corre 1 at i on be t ween the vo 1 ume of coal drilled out and the seismic seam reactions. Such a correlation is also obvious in a plot, where al 1 results of some 280 test-dri11ings are combined (figurę 8). Yet still there is a very high standard deviation, which shows that a much bigger number of measurements is needed to łmprove statistical evaluations. In order to make futurę measurements easier than before, the described eąuipment has been improved. It contains better ełec- tronics, which among other advantages for example allows a more exact on-line-evaluatłon of the energy values, and it is smaller