Evolution of bulk compressibility and permeability of granite due to thermal cracking

Granite samples were subjected to heating at different temperatures and rapid water cooling. Hydrostatic compression tests were performed on the thermally treated samples. The initial tangent bulk modulus was measured. The critical value of hydrostatic stress for closing thermally induced micro-cracks was identified and the residual volumetric strain after unloading was determined. Gas permeability of granite samples was also determined under different levels of hydrostatic stress. It is found that the density of thermally induced micro-cracks can be correlated with the residual volumetric strain, both increasing when the pre-treatment temperature is higher. There is a significant increase of gas permeability up to several orders of magnitude as a consequence of micro-cracks induced by the heating and water-cooling process.