Kaiser effect in tri-axial tests of limestone samples

The acoustic emission technique is normally used to observe the Kaiser or memory effect (KE) during uniaxial reloading of core samples. The Kaiser effect is observed as an increase in AE hit rate (number of AE signals per time unit). The memory effect is caused by fractures that have formed in a previous cycle, and only continue to grow further when the stress value reaches the previous maximum level. However, in situ stresses are not uniaxial. To take different triaxial stress states in different loading cycles into account two relationships, between the stresses in the previous cycle and the stress corresponding with the Kaiser effect, were theoretically developed. Both relationships are based on their own rock-dependent, dimensionless coefficient, respectively k(1) and k(2). The aim of the experiments presented in this paper is to evaluate both equations and to determine both coefficients for one type of rock material, being crinoidal limestone.