| Abstract |
This paper presents the effects of confining pressure on mechanical behavior of Phu Kradung sandstone which was subjected to monotonic and cyclic loading. The cylindrical specimens were core drilled into two directions which are normal and parallel (0 and 90 degree) to lamination planes, so the effect of loading direction could be observed. Monotonic and cyclic loading tests were conducted under unconfined and confined pressures at 6, 12, 20 and 30 MPa. The volumetric strain, lateral strain and axial strain were determined during cyclic loading tests. For the unconfined compression test, the axial and lateral strains were measured by electrical gauges. However, the mechanical gauge and oil volume change were used instead in confined compression tests. The results from both types of loading tests indicated that the confining pressures had a significant influence on the behavior of sandstone samples. With an increase in the confining pressures, the ultimate strength, axial strain and the number of cycles to failure increased. The residual axial strains of sandstone samples obtained at a confining stress state can be described as three deformational stages, namely, the initial phase, uniform velocity phase and accelerated phase. The effect of direction of loading in parallel to lamination renders higher ultimate strength than that of normal to lamination in both monotonic and cyclic loading. |
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