1993 Fiscal Year Final Research Report Summary
Initial Stress Measurements using Ultrasonics
| Project/Area Number |
04650438
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
基礎・土質工学
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
KOBAYASHI Shoichi Kyoto Univ., Fac.of Eng., Professor, 工学部, 教授 (90025908)
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| Co-Investigator(Kenkyū-buntansha) |
NISHIMURA Naoshi Kyoto Univ., Fac.of Eng., Assoc.Professor, 工学部, 助教授 (90127118)
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| Project Period (FY) |
1992 – 1993
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| Keywords | initial stress / acoustoelasticity / sing-around period / andesite / sandstone |
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| Research Abstract |
This is to estimate initial stress state in a rock mass using phase speed measurements in a bore-core. The principle of the technique is based on the fact that the phase speed of ultrasonics (elastic waves) varies according to stress state (acoustoelasticity). Although the method requires high prescision time measurement, it is easy to carry out. Using the results, we may estimate initial stresses.
Main results obtained are as follows :
1) Set-up of accurate time measurement system : We set up a system for the accurate time measurement utilizing a sing-around equipment. It is accurate enough for the experiments.
2) Relation between stress and phase speed of the longitudinal wave : In order to investigate the relation between stress and phase speed, we used cylindrical specimens of andesite (average compressive strength : 2,140kgf/cm^2) and sandstone (average : 520kgfcm^2) were supplied for uniaxial repeatedly increasing compression test. Longiotudinal wave speed in the axial and radial directions were measured throughout loadding and unloading. It is clearly recognized that phase speed of the longitudinal wave changes at the highest stress ever experience, as is observed as kaiser effect (we call it histeresis effect). Phase speed change in the radial direction is much clearer. The stress levels tested were within 15% and 50%, respectively for the andesite and the sandstone.
3) Estimation of initial stresses : Initial stress may be estimated within accuracy of 50kgf/cm^2 and 25kgf/cm^2 for andesite and sandstone, respectively, using the above-mentioned histeresis effects and test results from several specimens shaped from bore cores in such a way as the axis of the specimen is appropriately inclined from that of the bore core.
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