AN EXPERIMENTAL STUDY ON FRACTAL PORE SIZE DISTRIBUTION AND HYDRO-MECHANICAL PROPERTIES OF GRANITES AFTER HIGH TEMPERATURE TREATMENT

摘要

This study experimentally estimated the fractal pore size distribution of granites, which is then linked to the hydro-mechanical properties of rocks treated by temperatures that range from 25 degrees C to 900 degrees C. The mercury intrusion experiment was carried out to characterize the pore size distributions and the MTS815.02 triaxial testing system was used to investigate hydromechanical properties of rocks. Finally, the micro-CT scanning system and scanning electron microscope system were employed to exhibit the evolutions of microstructures of cracks that were then linked to the macroscopic hydro-mechanical properties. The results show that the pore size distribution of granites follows the fractal scaling law and the fractal dimension ranges from 2.45 to 2.94. The fractal dimension decreases significantly when the temperature increases from 25 degrees C to 100 degrees C and then holds a constant with continuously increasing the temperature to 400 degrees C. The fractal dimension slightly increases as the temperature increases from 400 degrees C to 500 degrees C and decreases following a linear relationship until the temperature of 900 degrees C. The porosity obtained by the mercury intrusion experiment shows an exponential relationship with the fractal dimension. Both the axial stain and peak total stain, as well as the initial permeability and the permeability at the peak axial stress, have quadratic functions with the fractal dimension. The mean aperture of fractures increases from 56.75 mu m to 76.10 mu m with increasing the temperature from 100 degrees C to 900 degrees C through micro-CT scanning. The scanning electron microscope test clearly shows that the fractures are generated when the temperature exceeds 300 degrees C, which agrees well with the micro-CT scanning results. With increasing the temperature from 400 degrees C to 900 degrees C, both the number and aperture of fractures increase, which well interprets that both the strain and permeability increase as indicated by the triaxial stress-flow tests.