Bryan-Jones, Alistair (1998) Evaluation of Rock Mass Behaviour using Borehole Microseismic Monitoring: An Application to Longwall Coal Mining. PhD thesis, University of Liverpool.
Full text not available from this repository.Abstract
In all mining regions in the world there are reports of earthquake induced by mining activity, which in some regions, for example Poland, can be as large as tectonic earthquake, and can cause serious damage and loss of human life. However, the majority of induced earthquake are much smaller, in fact they are rarely felt, and the study of these microearthquakes allows the response of a rock mass to excavation to be exterminated in detail. The observed response of the rock mass is able to validate other observations and the results of numerical and physical modeling, and hence increase our understanding of the processes causing seismic activity around excavations. This thesis presents the results of a mining induced seismicity study that had a number of aims. the main aim was to examine the behavior of a previously undisturbed rock mass during the excavation of a volume of coal. In addition it was necessary to evaluate and improve microseismic analysis techniques previously used by the Microseismology Research Group at the University of Liverpool and develop new analysis technique. These techniques are applied to a dataset recorded during microseismic monitoring of two phases of mining at Asfordby Colliery in Leicestershire. The Asfordby superpit was developed at a cost of 400 M Pound in a previously unexploited coalfield with the intention to supply a large proportion of UK coal. However, poor working conditions and catastrophic roof failure were experienced during the two phases of mining at Asfordby leading to the eventual abandonment of the mine. Induced seismic events were recorder by single three-component seismometers installed in boreholes drilled specifically for this project. The technique to locate the seismic events, by analyzing the P-wave particle motion, is a development of that used by previous studies. Improvement made are the introduction of location error estimation and ray tracing through 1-D layers velocity models. An analysis technique has been developed that examines seismic event locations and uses critically estimated errors to cluster the event locations and identify possible geological structures associated with the induced seismicity, thus simplifying the interpretation of the event locations. A method to determine double-couple source mechanisms from single three-component seisograms was a major development, and application of this method to the Asfordby data give considerable insight int the rock mass response to mining. The seismicity recorded during the first phase of mining revealed a rock mass behavior that has never been observed before in analogous studies, and was most like the fracture patterns predicted by a numerical model of lead to uncontrolled roof conditions and eventual catastrophic failure, and was observed several weeks prior to the first serious problems experienced at the face. Source mechanisms for the recorded seismic events further supported this interpretation and gave a detailed picture of the initiation and propagation of a major fracture. This observation has significance to the mechanics of fault initiation in unfractured rock. Serious weighting were experienced during this phase of mining, the timing of which correlated with induced seismicity. The seismicity recorded during the second phase showed a more typical response of the rock mass, as predicted by previous studies and physical and numerical models. Source mechanisms again supported this interpretation, and highlighted relationships between roof geology and induced seismicity. The observations made by the microseismic monitoring at Asfordby demonstrate that given real time processing of recorded seismic data, significant departures from the expected rock mass behavior cold be identified, and advance warning given of possible problems.
| Item Type: | Thesis (PhD) |
|---|---|
| Subjects: | Methodology > Method and procesing > Source parameter estimation Methodology > Method and procesing > Collective properties of seismicity Region > UK > Leicesterhire Inducing technology > Underground mining |
| Project: | EPOS-IP > ASFORDBY: underground coal mining |