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This test is carried out on saturated or unsaturated samples with cylindrical shapes from 1 to 1.5 inch in diameter. Specimen loaded in a Hoek cell and then static elastic constants are measured with increasing pressure or stress level. This test measures axial strain and horizontal strain due to loading of core. It should be noted that specimen is not failed. But at the beginning axial load is increased to some big value and then it is decreased to zero. So, the unloading curve is often used for determine the elastic constants since it is considered that on unloading no possible fracture of the grains will take place. Modulus of elasticity calculated as ratio between the axial load change and the axial strain changes at 50% failure stress:
| (4) |
It is used the central part of graph because this part is characterized with elastic rock properties in deep depth and there are all micro fractures are closed due to high value of lithostatic pressure.
Poisson’s ratio calculated from the ratio between the change in radial strain and the change in axial strain [1]:
| (5) |
The results of test are represented on the figures 5,6:
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| Figure 3. Machine with mounted specimen that uses in Brazilian test | | | Triaxial strength testing |