Coupling Effects of Strain Rate and Low Temperature on the Dynamic Mechanical Properties of Frozen Water-Saturated Sandstone

Abstract

The mechanical properties of water-rich rocks in a subzero temperature environment are quite different from those at room temperature, which introduces many unexpected engineering hazards. The dynamic compressive behaviors of frozen water-saturated sandstone are related to strain rate and temperature at different degrees. In this paper, quasi-static and dynamic tests were conducted on the saturated sandstone utilizing the MTS-816 apparatus and the modified split Hopkinson pressure bar (SHPB) device with a freezing module, which are constrained at a temperature range of −1 °C~−20 °C and a strain rate range of 10−5 s−1~200 s−1. The coupling effect of strain rate and temperature on the mechanical characteristics of saturated sandstone is systematically investigated. It is found that the quasi-static compressive strength of frozen saturated sandstone increases with the applied temperature from −1 °C to −5 °C and decreases with that from −5 °C to −20 °C, while the dynamic compressive strength exhibits an opposite trend. Different from the primary shear failure under quasi-static tests, the failure pattern of the frozen specimens becomes tensile failure under dynamic tests with an evident sensitivity to the applied temperature. Furthermore, the dissipated energy can be positively correlated with strain rate, while the growth rate of dissipated energy decreases with the applied temperature from −1 °C to −5 °C and increases with that from −5 °C to −20 °C. A new water-ice phase transition mechanism was further introduced, which divided the freezing process of water-saturated rock into the intensive stage and the stable water-ice phase transition stage. The underlying mechanism of water-ice phase transition governing the dynamic mechanical behavior of frozen saturated sandstone was also revealed.