Three case studies on the microseismic activities occured in deep coal mining panels are presented with their interpretations. It has been cleared from observation that the sequence of the seismic activities which can be represented by the change of the seismic energy release rate is substantially influenced by the geometry of excavations changing daily with mining activity. A simulation model has been developed to evaluate the stress distribution and the strain energy release rate which is defined as the total strain energy released from the newly fractured areas during the unit face advance of the mining front. Since this energy release rate has revealed to be in good correlation with the observed seismic energy release rate for each case study, the newly developed model could be applicable to interprete and to anticipate the fracturing phenomena occuring around the excavation.
Trois etudes de cas concernant les les activites microsismiques produites par l'extraction de charbon en profondeur sont presentees ici, ainsi que leurs interpretatione. Il ressort clairement des observations que la sequence de leure activites, qui peut etre representee par Ie changement du taux de degagement d'energie sismique, est influencee de façon substantielle par la geometrie des excavations, qui varient quotidiennement en fonction de l'activite miniere. Un modele de simulation a ete mis au point afin d'evaluer la distribution des forces et la taux du travail de deformation degage, qui est defini comme le total du travail de deformation degage des zones venant d'etre fracturees pondant la progression d'une unitè d'exploitation. Etant donne qu'il a ete revele que ce taux de degagement d'energie possede une bonne correlation avec le taux de degagement d'energie sismique observe dans chacune des etudes de cas, le modele qui vient d'etre mis au point pourrait etre utilise pour interpreter et prevoir les phenomenes de fracturation se produisant aux alentours de l'excavation.
Drei Fallstudien ueber mikroseismiche Bewegungen in tiefen Kohlengrubenfeldern sowie ihre Interpretationen werden vorgetragen. Aus Beobachtungen hat sich ergeben, daβder seismichen Aktivitatenablauf, der durch eine Änderung der Freisetzungsrate der seismichen Energie dargestellt werden kann, wesentlich von der Geometrie der sich taglich mit dem Abbau andernden Ausschachtungen abhangt. Ein Simulationsmodell wurde entwickelt, um die Druckverteilung und die Freisatzungerate der Formenderungsenergie zu bewerten, die als wahrend das Einheitsvortriebs der Abbaufront von den neu durchbrochenen Bereichen freigesetzte Gesamt-Formenderungsenergie definiert wird. Da diese Energiefreisatzungsrate mit der beobachteten seismichen Energiefreisatzungsrate fuer jede Fallstudie in guter Korrelation steht, konnte sich das neu entwickelte Modell auf die Interpretation und Prognose von Brucherscheinungen im Umkreis der Ausschechtung anwenden lassen.
Working area of Horonai coal mine, Japan, is now located about 1,100 meters below surface and strata control is one of the urgent tasks to be solved. For this purpose the measuring system to monitor the microseismic activities occurring around the excavating panels has been developed and applied in this mine in these ten years. A model study based on the stress analysis to simulate the rock mass fracturings induced around the excavation has also been Conducted along this line to interpret the monitoring data. In this paper, case studies are presented for the three panels on the observed seismic activities and their interpretations using the simulation model. In each panel, two adjacent slightly inclined coal seams, the upper seam and the lower seam separated by 10 meters distance, were extracted by the fully mechanized longwall mining method. There were no old workings below and above these observed panels, whose condition should often bring high stress state in the vicinity of the excavation and consequently high level of microseismicity.
The seismic activities are monitored by using the system developed by Sato et. al (1985) composed of ten velocity-type sensors positioned on the surface and in the ground around the monitored panels. The source location and the maximum amplitude of the ground velocity are determined for each event. From the latter the Richter's scale magnitude and the amount of seismic energy are evaluated using Gutenberg - Richter's formula and Muramatsu's empirical formula, respectively. The seismic energy data is further supplied to evaluate the seismic energy release rate which is defined as the total sum of its individual energy accompanied with the unit face advance. These data are processed to deliver graphs and contour maps which visualize the seismic activities in terms of mining progress and/or excavation geometry as shown in chapter 4.
There have been several proposals on the evaluation of energy changes accompanying mining. The most used of these associated with the interpretation of rock burst is the released energy which is defined, in case of tabular mining, as a half of the product of the load which applied to the element just before the excavation and the convergence of that portion removed by the excavation.
