RESIDUAL STRESS MEASUREMENTS BY THE DRILLHOLE PRESTRESSED METER AND THE RIGID BRASS PLUG
RESIDUAL STRESSES IN ROCK WERE MEASURED USING TWO ENTIRELY DIFFERENT INSTRUMENTS, NOT ONLY IN THEIR MECHANISM, BUT ALSO IN THE PRINCIPLES GOVERNING THEIR BEHAVIOR IN RELATION TO THE RESIDUAL STRESSES IN THE ROCK. THE DRILLHOLE PRESTRESSED METER, DEVELOPED BY HAWKES OF SHEFFIELD UNIVERSITY, OPERATES ON PHOTOELASTIC PRINCIPLES. THE CHANGE OF STRESS IN THE GLASS CYLINDER, DIAMETRICALLY LOADED BETWEEN THE WALLS OF A DRILLHOLE, CONSEQUENT UPON THE RELIEF OF STRESS BY OVERCORING IS OBSERVED AS THE CHANGE OF FRINGE ORDER IN THE PHOTOELASTIC PATTERN. THIS IS ESSENTIALLY A NON-RIGID INSTRUMENT. BY A PROCESS OF CALIBARATION IN THE LABORATORY THE FRINGE ORDER CAN BE RELATED TO STRAIN, AND TAKING ACCOUNT OF THE MODULUS OF ELASTICITY OF THE ROCK THE RESIDUAL STRESS IN THE PLANE OF THE PRESTRESS CAN BE DETERMINED. THE ADVANTAGES OF THIS DEVICE ARE EASE OF OPERATION, THE ISOCHROMATIC PATTERN BEING SIMPLE AND EASILY READ WITHOUT EXPERTISE IN PHOTOELASTICITY, FREEDOM FROM ELECTRONICS, AND ROBUSTNESS. A FURTHER ADVANTAGE IS THAT THE INSTRUMENT IS LOCKED INTO THE DRILLHOLE BY ITS WEDGING ACTION AND SO HELD FIRMLY AGAINST VIBRATION BY THE OVERCORING BIT. THE RIGID BRASS PLUG, DEVELOPED BY THE MINING RESEARCH ESTABLISHMENT, OPERATES AS A SOLID INCLUSION IN INTINATE CONTACT WITH THE WALLS OF THE DRILLHOLES. IT IS AN UNI-AXIAL STRESS METER IN WHICH THE CHANGE IN STRAIN ON OVERCORING IS MEASURED BY MEANS OF FOIL STRAIN GAUGES SET ACROSS THE DIAMETER OF THE CYLINDRICAL PLUG. PROVIDED THE MODULUS OF ELASTICITY OF THE ROCK IS LESS THAN ABOUT HALF OF THE PLUG, THE STRESS INDUCED INTO THE PLUG WILL BE LARGELY INDEPENDENT OF THE MODULUS OF THE SURROUNDING ROCK. CONSEQUENTLY, ACCURATE KNOWLEDGE OF THE MODULUS OF ELASTICITY OF THE MEDIAN IS NOT REQUIRED. THIS IS THE CHIEF ATTRACTION OF THIS METHOD.
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Supplemental Notes:
- Vol 2, pp 3-7, 3 FIG, 1 TAB, 4 REF
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Authors:
- HOBBS, N B
- CLARKE, D A
- Publication Date: 1966-9
Media Info
Subject/Index Terms
- TRT Terms: Boreholes; Measurement; Measuring instruments; Modulus of elasticity; Photoelasticity; Prestressing; Residual stress; Rocks; Strain gages; Stresses
- Old TRIS Terms: Stress conditions (Soil)
- Subject Areas: Geotechnology; Highways;
Filing Info
- Accession Number: 00234316
- Record Type: Publication
- Files: TRIS
- Created Date: Apr 2 1994 12:00AM