Shigen-to-sozai, Vol.116, No.12, pp.972-978.
Damage of Rock Core due to Tensile Stresses
during Boring under In-situ Stresses and
its Relation to DSCA
Koji MATSUKI1, Wataru IINO1 and Kiyotoshi SAKAGUCHI1
| 1. Department of Geoscience and Technology, Graduate School of Engineering, Tohoku University, Aoba-ku. Sendai 980-8579 |
| The maximum tensile stress experienced by
an HQ core in an arbitrary horizontal cross
section was accumulated in equal area stereonet
for 77 stress conditions. The maximum tensile
stress accumulated for a central area of
the core (57.1 % of the total area) was concentrated
in a certain direction, which was nearly
the direction of the minimum principal stress
s3, for all stress conditions except those
in which s2＝s3. Based on the assumption that a penny shaped
crack is produced normal to the maximum tensile
stress at each point of a horizontal cross
section in proportion to the magnitude, the
crack density in the core was analyzed by
calculating strains under hydrostatic pressure
as in Differential Strain Curve Analysis
(DSCA). The direction of the maximum crack
density was similar to that of the accumulated
maximum tensile stress. Thus, the direction
of the maximum crack density obtained by
DSCA predicts the direction of the minimum
principal stress rather than that of the
maximum principal stress, if the distribution
of pre-existing microcracks before stress
relief is isotropic and if additional microcracks
are produced by merely the tensile stresses
during boring under in-situ stresses. To verify this, the crack density was measured by DSCA for two cores of quartz diorite, which were taken by overcoring when a hemispherical ended borehole technique, one of stress relief method, was applied to measure in-situ stresses at Kanetsu tunnel. The direction of the maximum crack density obtained by DSCA was nearly that of the minimum principal stress for both cores. |
| KEY WORDS: Crack Density, Tensile Stress, DSCA, Damage of Rock Core, Boring Under Stresses |