Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006geoji.167.1425s&link_type=abstract
Geophysical Journal International, Volume 167, Issue 2, pp. 1425-1438.
Astronomy and Astrophysics
Astronomy
Downhole Logging, Instrumentation, Residual Stress, Rheology, Stress Distribution, Thermal Conductivity
Scientific paper
Quantitative determination of crustal stress states remains problematic; here we provide a synopsis of work that is leading towards the development of an optical interferometric method that may be applied in boreholes. The major obstacle to the continued development of this technique has been the problem of determining the state of stress within a stressed continuum; we demonstrate the solution of both the technical and analytical issues in this contribution. Specifically, dual beam digital electronic speckle interferometry is used to record the stress-relief displacements induced by the drilling of blind holes into blocks subject to uniaxial compressive stresses. Speckle interferograms are produced at rates near 4 Hz using a local Pearson's correlation method and are stored for analysis. This time-lapse capability is useful when transient effects, such as thermal expansion displacements produced by the heat of drilling or ongoing time-dependent deformation, are active. Four acrylic blocks subject to uniaxial compressions from 3.8 to 5.5 MPa with the compressions oriented at different angles with respect to the axes of the interferometry system were studied. Relative fringe phase information was extracted from appropriate interferograms and inverted to provide a quantitative measure of the 2-D stress field within the block. In general, the largest value of the stress obtained in the inversion agreed with the known stress to better than 70 per cent. These measurements suggest the levels of uncertainty that might be expected by use of such optical interferometric techniques. This technique may show promise for quantitative stress determination in the earth to complement existing techniques. As well, while the interferometric principles are not exactly the same as for the popular satellite-based INSAR techniques, the optical method here has the potential to be useful in analogue physical model laboratory studies of deformation in complex structures.
Diallo Mamadou S.
Schmitt Douglas R.
Weichman Frank
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