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Core Discing
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Core
disking has long been recognized as an indicator of high in
situ stress in the earth's crust (Jaeger
and Cook, 1963). Field evidence suggests that core disking
in vertical boreholes is the result of high horizontal stresses.
The correlation
found in the field has been between the trough axis of the
saddle shaped disks and the direction of the maximum horizontal
stress. The morphology of the surfaces of the detached disks,
examined by a Scanning Electron Microscope (SEM), reveals
a set of lineations in the direction of the maximum horizontal
stress (Haimson and Lee, 1995). Both
the saddle shape and the lineation markings on the surface
of the core disks, as observed in the SEM, can serve as additional
indicators of the maximum horizontal stress direction.
On the
other hand, laboratory tests suggest that despite considerable
scatter there is a consistent decline in the average disk
thickness with increase in maximum horizontal stress (Haimson
and Lee, 1995). The usefulness of core disking is in being
complementary to other stress indicators and stress measurements
both for establishing principal stress directions and for
indicating far-field stress magnitudes.
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| Dyke,
C. G. Core disking: its potential as an indicator of principal
in situ stress directions. in V. Maury & D. Fourmaintraux
(eds.), Rock at Great Depth: 1057-1064. Rotterdam: Balkema
(1989).
Haimson,
B.C. and M. Lee, Estimating in situ stresses from borehole
breakouts and core disking - experimental results in
granite, Proceedings of the International Workshop on
Rock Stress Measurement at Great Depth, The 8th International
Congress on Rock Mechanics, Tokyo: Balkema (1995).
Haimson.
BC and M.Y. Lee, Borehole breakouts and core disking
and their complementary roles as in situ stress indicators;
an initial laboratory study. EOS - Trans. Am. Geophys.
Union. 75: 677 (1994).
Jaeger,
J. C. and N. G. W. Cook, Pinching-off and disking of
rocks, J. Geophys. Res. 68: 1659-1765 (1963).
Lehnhoff, T.F., T.K. Stefansson and T.M. Wintczak, The
core disking phenomenon and its relation to in-situ
stress at Hanford, SD-BET-T1-885, Rockwell Hanford Operations.
Washington (1982).
Obert,
L. & D.E. Stephenson. Stress conditions under which
core disking occurs, SME Transactions, 232: 227-235
(1965).
Stacey, T.R., Contribution to the mechanics of core
disking. J. S. Afr. Inst. Min. Met. 82: 269-275 (1982).
Sugawara,
K., Y. Kameoka, T. Saito, Y. Oka and Y. Hiramatsu, A
study on core disking of rock, Journal of Japanese Association
of Mining, 94: 19-25 (1978).
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