Microstructural analysis of granite tested under uniaxial compression conditions

Summary

Abstract

Detailed knowledge of the microstructural damage before, during, and after loading is crucial for a better understanding of the mechanisms leading to macroscopic failure of crystalline rocks. This is particularly true for granite, which is being discussed (Germany) or has already been selected (Finland, Sweden) as a potential host rock for final nuclear waste disposals. Therefore, it is important to evaluate the long-term stability and integrity of such subsurface storage systems in granite. This study examines the microstructures of uniaxially loaded granite up to 40 %, 60 %, 80 %, nearly 100 % and beyond of its maximum uniaxial compressive strength. Deformed granite specimens were saturated in colored epoxy resin before thin sections were prepared from central parts of the cylindrical specimens. The results indicate an increase in number of cracks with increasing maximum axial stress. The resulting crack pattern shows larger main fractures and fine inter- and intragranular cracks. Both tensile and shear cracks were identified, with tensile cracks dominating in all thin sections. Microfractures preferentially develop along pre-existing zones of weakness, such as grain boundaries or cleavage planes of biotite minerals. Finely ground mineral grains occur in areas of significant damage. These results provide valuable insights into the micromechanical processes of crack initiation and propagation in uniaxially loaded granitic rock samples. They improve the understanding of the mechanical stability of a potential host rock and serve as a basis for further numerical simulations to describe and predict failure mechanisms.