Application of the Full-Field Strain Measurement to Study the Kaiser Effect in Granite Under Indirect Tensile Loading
Authors: Ali Z. , Karakus M. , Nguyen G. D. , Amrouch K. 
Published: September 2022

ABSTRACT:
In-situ stresses and their spatial distribution are important parameters in analyzing and designing underground structures. Deformation rate analysis (DRA) and acoustic emission (AE) are methods of in-situ stress measurement from oriented core, which take advantage of the stress memory in rocks, also known as the Kaiser effect. However, locating point of inflection can be problematic in both DRA and AE analyses due to the rock heterogeneity and complex geological paleo-stress history. This paper investigates the Kaiser effect under indirect tensile loading and the application of full field strain measurement for locating the point of inflection in deformation rate analysis. Cyclic loadings were performed on Brazilian disc specimens of Adelaide black granite and the deformation process was monitored using digital image correlation (DIC) and AE monitoring system. The tests were conducted with and without rotating the disc specimens between the successive loading cycles. The directional dependency of the Kaiser effect was studied by rotating the specimens at 15 degrees interval between 0 and 90 degrees. Strain localization and its influence on the bending point in DRA and stress memory were also investigated. Results show that Kaiser effect exist under indirect tensile loading and rotation of principal axis do not influence the Felicity Ratio (FR). The characteristic DRA curves were influenced by the strain distribution in the specimens which is more pronounced in the localized region.

1. INTRODUCTION
The rock stress memory also known as the Kaiser effect is a unique property in rocks to store, retain and reproduce information about the previously applied stresses and strains Kaiser, (1953); Lavrov (2002). This characteristic of the rocks has been widely studied for its application as a non-destructive method for in-situ stress measurement from oriented cored rocks Seto et al. (1999); Villaescusa et al. (2001); Karakus (2014); Ali et al. (2021). However, the viability of the method for stress measurement is still being questioned because there have been studies showing that the Kaiser effect is influenced by numerous factors such as the duration of load applied Filimonov et al. (2001); Lavrov (2003), time delay Kanagawa et al. (1995); Jin et al. (2009), water saturation and heating Yoshikawa and Mogi (1981); Lavrov (2002), rotation of principal axis Stuart et al. (1993) and the coring process Sakaguchi et al. (2002). Moreover, it is also argued that laboratory conditions are different from in-situ conditions, which is more complex and includes not only the compressive stresses but also tensile stresses Lehtonen et al. (2011); Zhang et al. (2017); Chen et al. (2018); Ban et al. (2020). In addition, the complications associated with the stress redistribution after excavation can raise further questions on the application of techniques for stress measurement. The stress zones with the concentration of tensile stress surrounding excavation together with rock tensile properties can play an important role in the stability of the structures. It is for this reason very important to investigate the application of these techniques under tensile loading and understand their characteristics.