Mikashakar Nntp essai triaxial pdf Hydrostatic, triaxial, proportional and oedometric tests are performed and show the influence of the loading path on the compaction process. Cement and Concrete ResearchElsevier,38 3pp A triaxial compression test consists in imposing on the testtube a vertical radial force all while keeping the side pressure constant. A triaxial press of high capacity is used to characterize the triaxial behaviour of concrete according to various loading paths. Measurement of the coefficient of permeability for a. Triaxial behaviour of concrete under high stresses: Thomas Gabet 1 AuthorId: The aim of this study is to characterize the behaviour of concrete under high triaxial loading at levels of confinement and axial stress of the order of the GigaPascal.
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Test execution[ edit ] For soil samples, the specimen is contained in a cylindrical latex sleeve with a flat, circular metal plate or platen closing off the top and bottom ends. This cylinder is placed into a bath of a hydraulic fluid to provide pressure along the sides of the cylinder. The top platen can then be mechanically driven up or down along the axis of the cylinder to squeeze the material. The distance that the upper platen travels is measured as a function of the force required to move it, as the pressure of the surrounding water is carefully controlled.
Rock[ edit ] For testing of high-strength rock, the sleeve may be a thin metal sheeting rather than latex. Triaxial testing on strong rock is fairly seldom done because the high forces and pressures required to break a rock sample require costly and cumbersome testing equipment. Effective stress[ edit ] The effective stress on the sample can be measured by using a porous surface on one platen, and measuring the pressure of the fluid usually water during the test, then calculating the effective stress from the total stress and pore pressure.
Triaxial test to determine the shear strength of a discontinuity[ edit ] The triaxial test can be used to determine the shear strength of a discontinuity. A homogeneous and isotropic sample fails due to shear stresses in the sample. If a sample with a discontinuity is orientated such that the discontinuity is about parallel to the plane in which maximum shear stress will be developed during the test, the sample will fail due to shear displacement along the discontinuity, and hence, the shear strength of a discontinuity can be calculated.
The rate of axial deformation is kept constant, i. The idea is that the test allows the sample and the pore pressures to fully consolidate i. The test may take a long time to allow the sample to adjust, in particular low permeability samples need a long time to drain and adjust strain to stress levels. The shear characteristics are measured under undrained conditions and the sample is assumed to be fully saturated.
Measuring the pore pressures in the sample sometimes called CUpp allows approximating the consolidated-drained strength. Shear speed is often calculated based on the rate of consolidation under a specific confining pressure whilst saturated. Confining pressures can vary anywhere from 1 psi to psi or greater, sometimes requiring special load cells capable of handling higher pressures. The sample is compressed at a constant rate strain-controlled. True triaxial test[ edit ] Triaxial testing systems have been developed to allow independent control of the stress in three perpendicular directions.
This allows investigation of stress paths not capable of being generated in axisymmetric triaxial test machines, which can be useful in studies of cemented sands and anisotropic soils. The test cell is cubical, and there are six separate plates applying pressure to the specimen, with LVDTs reading movement of each plate.
The apparatus is significantly more complex than for axisymmetric triaxial tests, and is therefore less commonly used. Free end condition in triaxial testing[ edit ] The Danish triaxial in action Triaxial tests of classical construction had been criticized for their nonuniform stress and strain field imposed within the specimen during larger deformation amplitudes.
To test specimens during larger deformation amplitude, "new"  and "improved"  version of the triaxial apparatus were made. Both the "new" and the "improved" triaxial follow the same principle - sample height is reduced down to one diameter height and friction with the end plates is canceled. The classical apparatus uses rough end plates - the whole surface of the piston head is made up of rough, porous filter.
In upgraded apparatuses the tough end plates are replaced with smooth, polished glass, with a small filter at the center. Due to extremely uniform, near isotropic stress field - isotropic yielding takes place. During isotropic yielding volumetric strain is isotopically distributed within the specimen, this improves measurement of volumetric response during CD tests and pore water pressure during CU loading.
Also, isotropic yielding makes the specimen expand radially in uniform manner, as it is compressed axially. This is in contrast with classical setup, where the specimen forms a bugle in the center, while keeping a constant radius at the contact with the end plates. Post-liquefaction testing. The fine sand specimen was liquefied during CU cycles and recovered with CD cycles many times.
The wrinkles formed due to extreme volume change imposed by iterating between CU liquefaction and draining. In liquefied state sample become soft enough to imprint thin latex. During CD cycles - stiff enough to preserve the imprinted pattern. No bulging or shear rupture is present despite numerous instances of pure plastic yielding. The "new" apparatus has been upgraded to "the Danish triaxial" by L. It provides improved measurements of volumetric response - as during isotropic yielding, volumetric strain is distributed isotopically within the specimen.
Isotropic volume change is especially important for CU testing, as cavitation of pore water sets the limit of undrained sand strength. The load cell is submerged and in direct contact with the upped pressure head of the specimen.
Deformation transducers are attached directly to the piston heads as well. Control of the apparatus is highly automated, thus cyclic loading can be applied with great efficiency and precision. The combination of high automation, improved sample durability and large deformation compatibility expands the scope of triaxial testing.
The Danish triaxial can yield CD and CU sand specimens into plasticity without forming a shear rupture or bulging. A sample can be tested for yielding multiple times in a single, continuous loading sequence. Samples can even be liquefied to a large strain amplitude, then crushed to CU failure.
CU tests can be allowed to transition into CD state, and cyclic tested in CD mode to observe post liquefaction recovery of stiffness and strength. Test standards[ edit ] The list is not complete; only the main standards are included.
Le problme dans les sols consiste tablir cette rsistance. Lchantillon, les conditions de lessai et le type de lessai doivent reprsenter le plus possible les conditions du problme quon veut tudier. Le matriau est disponible dans un certain tat Quel est sa rsistance mobilisable dans cette situation. Le principal problme en stabilit des pentes : quel est la rsistance du sol pour les conditions donnes fin de construction, long terme, vidange rapide, sollicitation dynamique, etc. De quoi va dpendre la rsistance dun sol? En ralit le problme est beaucoup plus complexe si on regarde louvrage dune faon gnrale et universelle.
Essai bi-axial et tri-axial sur biomatériaux
Sar Cement and Concrete ResearchElsevier,38 3pp Multiple failure state and strain controlled triaxial tests 19 the advantage friaxial the above new test procedures, in comparison with the conventional test, is that from one specimen more information is. Wednesday, December 19, — 3: Tuesday, October 20, — 5: Triaxial behaviour of concrete under high stresses: The material has been tested in three conditions: Influence of the loading path on compaction and limit states. Wtna triaxial compression test notdrained with a. A triaxial compression test consists in imposing on the testtube a vertical radial force all while keeping the side pressure constant.