Experimental research on the influence of loading rate on the mechanical properties of limestone in a high-temperature state

Engineering problems associated with high-temperature rock, such as the deep disposal of high-level radioactive nuclear waste, underground gasification and storage of coal, development of geothermal resources, restoration of important buildings after a fire, among others, have drawn the interest of many engineers and become a new and developing field of rock mechanics. In our study, we conducted the uniaxial compression test under conditions of high temperatures (T) that range from 20 degrees C to 800 degrees C and loading rates (l(r)) that vary from 0.001 to 0.1mm/s, using the MTS 816 rock mechanics testing system, with the aim to investigate the evolution of deformation and intensity parameters of the limestone. The results show that the uniaxial compression process of limestone at different temperatures and loading rates comprises four stages: compaction, flexibility, yielding and post-peak failure. With increasing temperature, the ductility of limestone, the peak strain and the maximum strain after failure increase, and the post-peak softening characteristics of limestone gradually become obvious; however, the peak stress and elastic modulus of limestone decrease gradually. With increasing loading rate, the slope of the stress-strain curve in the elastic stage increases, and the deformation and intensity parameters of limestone increase accordingly. At T500 degrees C and l(r)0.01mm/s, the rock specimens undergo failure or tension-shear mixed failure. At T>500 degrees C and l(r)>0.01mm/s, Y-shaped shear failure occurs in the rock specimens. The failure degree of the limestone becomes more severe with increasing temperature and loading rate. The results of this study provide a scientific basis for high-temperature rock engineering studies on the design and construction of deep geological underground storage areas for high-level radioactive nuclear wastes, geothermal development, among others.