Thermomechanical characterization of two Jalore granites with different grain sizes for India’s HLW disposal

Abstract

The time-dependent temperature distributions in the deep geological repository must be carefully designed for high-level radioactive waste (hlw). Therefore, for the main purpose of this study, we carried out a laboratory investigation of the physical and mechanical properties of the two jalore white and red granitic rocks with variable grain sizes at different heating rates (3, 5, 10, and 15 °c/min). After heat treatments, micro- and macrocracks are readily observed in coarse-grained red granite, whereas no significant cracks were observed in fine-grained white granite. As heating rates increased, the number of intergranular cracks in the red and white granite increased. When the heating rate was more than 10 °c/min, in coarse red granite specimens, separate grains can be observed and the tensile mode of failure was dominated by thermally induced cracks. Microscopic observations revealed mainly intergranular microcracks in quartz, the opening of cleavage plains, and deformation in biotite in red granite due to mismatched thermal expansion. Biotite produces a concentration of stresses along its grain boundaries. In contrast, the thermal expansion anisotropy of quartz, the microstructure of rocks with large amounts of quartz, does not necessarily experience large stresses in white granite. Increases in tensile strength were less significant for coarse-grained red granite specimens than for fine-grained white granite specimens. The results can be used to identify the deformation and failure analysis of host rock for india’s hlw disposal sites. © 2022, springer-verlag gmbh germany, part of springer nature.