Detection of Kaiser Effect in Marbles under Tensile Stresses

Rock Engineering 2009 - Rock Engineering in Difficult Conditions
Carlos Dinis Da Gama, Qiang Xie, Xianbin Yu, Yuxin Chen,
Abstract Kaiser effect was noticed while submitting marble samples to cyclic tensile stresses. An automatic data acquisition system was applied through analog to digital conversion upon recording analog signals of stress, strain and acoustic emission (AE) emitted from Portuguese marble specimens under diametrical and bending loadings in successive loading cycles. Results confirm that the Kaiser effect was detected in both cases with a felicity ratio that varied from 0.92 to 1.2, meaning that it is possible to measure the pre-existing stresses in rocks under complex states of stress by means of other tests besides uniaxial compression. It was found that Kaiser effect in bending tests was more pronounced than that in Brazilian tests which is due to the fact that stress distribution and crack propagation in Brazilian tests are more complex than those in bending tests. Results also show that cumulative AE events vs. stress curve is more suitable for Kaiser effect recognition than cumulative AE energy vs. stress curve, as every event has different scales of energy. Furthermore, four types of AE curves are proposed for further AE investigations and the intrinsic behavior of rock should dominate the choice of testing method, i.e. compression tests to address “in situ” stress logging and bending tests to support roof stability problems.
Keywords: Kaiser effect, Bending, Acoustic Emission (AE), Marble, Brazilian Test
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