Dynamic mode I fracture properties of saturated white sandstone under ambient sub-zero temperatures

Dynamic fracture properties of frozen rocks are essential for better designs of rock engineering infrastructures in cold regions. Thus, a dynamic-cryogenic testing system combined with a high-speed camera is adopted to conduct dynamic tests under ambient room and sub-zero temperatures (20 °C, −10 °C, −20 °C, and −30 °C). A porous white sandstone (WS) is used to fabricate notched semi-circle bend (NSCB) specimens for mode I dynamic fracture tests. The percentage of ice and unfrozen water in rock pores under different temperatures is quantified using the nuclear magnetic resonance (NMR) method. For comparison purpose, dry specimens are also tested under the same ambient temperatures. The results show that the dynamic fracture toughness (DFT) for two sets of specimens all show obvious rate dependency. Except for −30 °C, DFTs of dry specimens are marginally influenced by the sub-zero temperatures. On the contrary at a given loading rate, DFT of frozen saturated specimens first drops to the lowest value at −10 °C before further increasing with the dropping ambient temperature. Compared with dry specimens, saturated specimens show lower DFTs and crack propagation velocities that are quantified with the digital image correlation (DIC) method. The experimental results are explained invoking the rock weakening and enhancing mechanisms of the ice and unfrozen water mixture in rock pores. These results are useful to blasting designs in cold areas.