Observations of shear-wave splitting in signals from a controlled seismic source have never previously been used to parameterise a rockmass in a mine environment. In developing the necessary processing and modelling techniques and interpreting the final results, I demonstrate the usefulness of such a controlled-source shear-wave experiment to parameterise non-destructively a granite rockmass <I>in situ</I> and monitor non-destructively the effects of excavation. A Schmidt Hammer is used to pulse the free end of a nylon rod inserted down a 40cm borehole to create the seismic signals. I show the resulting seismograms to be highly reproducible, with cross-correlation coefficients of 0.90 or greater resulting for repeated raypaths, and that the shear-wave motion produced matches that due to an infinitesimal, isotropic, directional point source. I demonstrate that the use of multiple source orientations of a known source for repeated raypaths greatly improves the reliability of picking shear-wave polarisations and time delays. Thus the use of multiple source orientations of a known source is highly desirable in any controlled source shear-wave experiment. I demonstrate the use of cross-correlation to be effective in detecting temporal changes and that particle motions need only be displayed on the planes perpendicular to the source-receiver directions when interpreting changes in shear-wave particle motions, which is convenient for large datasets. I identify temporal changes due to the advancement of the zone of excavation disturbance, which suggests that Extensive-Dilatancy Anisotropy is at least partially responsible for the <I>in situ </I>anisotropy. An increase in the strength of anisotropy suggests that excavation creates an anisotropic fabric of dry cracks with orientations governed by either the <I>in situ</I> stress field or mineral alignment. These results suggest that shear waves may be used to remotely monitor a rockmass.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:652520 |
| Date | January 1995 |
| Creators | Holmes, Gordon Murray |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/14088 |
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