MICROFRACTURING PROCESS AND FAILURE ZONE DEVELOPMENT IN JOINTED AMPHIBOLITE ROCK AS OBSERVED FROM ACOUSTIC EMISSION SOURCE LOCATIONS AND SURFACE-STRAIN MAPPING
K. Shivakumar, M. V. M. S. Rao*, K. Kusunose**, T. Satoh** and O. Nishizawa** National Institute of Rock Mechanics, Kolar Gold Fields, India *National Geophysical Research Institute, Hyderabad 500 007, India **Geological Survey of Japan, Tsukuba, Japan
Keywords: NDT, Acoustic Emission, Surface strain Monitoring, amphibolite rock, creep
ABSTRACT
Multichannel acoustic emission and surface strain monitoring were concurrently carried out successfully during the deformation of an amphilbolite rock containing a vertical joint until its failure. The experiment was performed under triaxial compression by setting the dilatant rock to failure through a single-stage creep [Experimental tests and data processing were carried out at the Geological Survey of Japan, Tsukuba, Japan under an India-Japan S & T collaboration project]. Post-data processing and analysis have helped in achieving 3-D source locations of AE and surface strain mapping, besides velocity anisotropy changes in the test sample. The results have revealed several interesting features of the various stages of microfracturing process and its micromechanics in terms of the formation, growth and migration of AE clusters; fractal structure of AE hypocenter distribution; and polarity of P-wave first motion; besides establishing excellent correlations between dilatant strain, AE activity and velocity changes during loading and creep regimes of the test sample. The determination and analysis of the spatio-temporal distribution of AE hypocenters has helped in tracking and characterizing the sequential development of failure zone that ran across the vertical joint in the amphibolite rock during the tertiary phase of creep.
Publication Source: Trends in NDE Science & Technology; Proceedings of the 14th World Conference on Non-Destructive Testing, New Delhi, 8-13 December 1996.Vol. 4, pages 2459 - 2462 Publisher:Ashgate Publishing Company
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