Measuring and testing – Specimen stress or strain – or testing by stress or strain... – By loading of specimen
Patent
1993-07-23
1995-01-10
Williams, Hezron E.
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
By loading of specimen
73816, 73821, G01N 308
Patent
active
053796454
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a test cell suitable for use in triaxially
loading cylindrical material specimens especially rock samples but not exclusively.
Conventional test cells for triaxially loading test specimens apply a more or less uniform radial pressure or confining stress and an axial stress. A Hoek cell, for instance, applies axial stress on the two ends of a cylindrical specimen, while the radial stress is developed by pressurizing a hydraulic fluid such as oil, around the cylindrical surface of the specimen, in a test cell body in which the specimen is held. It will be seen that the radial stress is angularly uniform i.e. the same in all radial directions and the only variations possible in relation to differential stress loading are axial and radial (angularly uniform) relative to each other. Test data from the field has shown though that the radial stress, more usually referred to as the horizontal stress, is defined by two principal stresses and is asymmetrical. The horizontal stress applied by a Hoek cell is symmetrical and as such not suitable for use in for example well break-out, shear wave splitting and fracture propogation testing. In order that specimens may be tested with asymmetrical, horizontal stresses it has been necessary to prepare cubes of test material which much more accurately reflect the principal stresses encountered in an actual three dimensional situation. Such cuboid samples are however more difficult and expensive to prepare and test, furthermore cuboid samples are not generally preparable from the cylindrical test specimens (approx. 100 mm dia.) normally obtained by conventional coring techniques used for sample recovery e.g.in the petroleum industry where boreholes are sunk to depths of 3000 m.
It is an object of the present invention to avoid or minimize one or more of the above disadvantages.
The present invention provides a test cell suitable for use in applying directionally variable three dimensional stress fields to a polygonal--section test specimen which test cell comprises a cell body having a barrel extending therethrough formed and arranged for receiving a said test specimen therein, said barrel having an array of elongate tubes disposed in side-by-side relation lining the inside wall of said barrel, said tubes having flexible side walls and being formed and arranged for connection, in use, to a pressurized fluid supply means, said test cell including control means formed and arranged for supplying at least one said tube with pressurized fluid at a different pressure to that in another said tube thereby to provide an angularly variable radial pressure loading on a said test specimen mounted in said barrel.
It will be understood that the polygonal-section barrel may have any number of sides, including an infinite number of sides as in, for example, a cylindrical barrel which is generally preferred for strength and ease of manufacture of the test cell. In use of a cylindrical bore, said tubes may be mounted on said inside wall so as to be in side-by-side contact with each other. Preferably at least one of said inside wall and said multiplicity of tubes is provided with adhesion means formed and arranged to secure said tubes to said inside wall.
Preferably the inside wall of said barrel has a multiplicity of elongate grooves formed and arranged for locating said elongate tubes in side-by-side relation. Most preferably said grooves are more or less `U`-shaped and said tubes have at least a more or less similarly shaped cross section formed and arranged to fit into said `U`-shaped groove. Desirably said `U`-shaped grooves are formed and arranged so as to permit tubes located therein to be in substantially direct contact with adjacent tubes.
It will be understood that the less space available for said tubes to expand into, when under pressure, the greater the pressure that may be applied over and above the normal rated unconfined capacity of the tube. Preferably the pressure differential attainable between adjacent tubes is at least 7000 kPa, advantageous
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patent: 5226310 (1993-07-01), Steiger
Abstract-Test device of ground samples-has stamp and base made of central and sprung circular sections to ensure shear during compression, Gosstroi Cons Eng, Apr. 11, 1986, SU-054972.
Heriot-Watt University
Olsen James M.
Williams Hezron E.
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