Experimental Study on the Kaiser Effect of AE under Multiaxial Loading in Granite

Abstract

Knowledge of the in-situ stresses is essential for underground excavation design, particularly in evaluating stability of excavation. Acoustic Emission method, which utilizes the Kaiser effect, is one of the simple methods for measuring in-situ stresses. Experiments on the Kaiser effect has been carried out under uniaxial compression and triaxial compression (σ1 > σ2 = σ3), but has not been carried out under the three different principal stresses (σ1 > σ2 > σ3). In this study, we performed two experiments on the Kaiser effect under multiaxial loading, using a hollow cylindrical granite specimen. The rapidly increasing point of cumulative AE event count was determined as the peak point of AE event count rate increment (AERI). The main results are summarized as follows. (1) In the case of the cyclic incremental σ1 loading under σ2≠σ3, the large peak point of AERI appeared just before the pre-stress level. And as more stresses prior to just before the peak point were estimated, the estimated error showed a tendency to increase. (2) In the case of re-loading under the lower σ2 and σ3 more than pre-loading, the estimated stresses using the three peak points of AERI corresponded to the pre-differential stresses (σ1-σ2), (σ1-σ3) and pre-axial stress σ1. The magnitudes of the three principal stresses were estimated under multiaxial loading from the Kaiser effect, using only one specimen.