Study on the kaiser effect of rock-like materials under triaxial compression

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The aim of this project is to compare the Kaiser effect of rock-like materials using triaxial compression test wit husing uniaxial compression test for the specimens pre-loaded under triaxial compression. Triaxial compression tests of Ogino Tuff were carried out under constant strain ratio and the AE activities were measured. Two AE sensors were put the inside of the upper and lower loading plates respectively. Three series of the experiments is as follows ; (1) Observation of the AE activities of rocks under Hydrostatic pressure. (2) The Kaiser effect under triaxial compression. (3) Estimation of the previous stress using uniaxial compression test by the small size specimens(PHI30X60mm) which were made of a large size specimen(PHI100mmX200mm) per-loaded under triaxial compression. These small size specimens were drilled to the three directions, that is, parallel, direct and 45 degree to the axis of the large size specimen.The experimental results and concluding remarks are as follows : (1) The Kaiser effects under hydrostatic pressure(25,50 kgf/cm^2) were observed at each stress level. (2) The accuracy of the estimated previous triaxial stress value using triaxial compressive pre-loading is better than the uniaxial one. Especially, the Kaiser effect of small specimen drilled to the direction of the maximum shear stress is not still satisfactory. (3) From the above results (2), if one the principal stress axis coincides with the speciemn axis, the accuracy of the estimated previous stress using the Kaiser effect on uniaxial compression test is satisfactory to a certain degree.