Comparative analysis of static and dynamic split tensile properties of red sandstone after freeze-thaw cycles

It's of great value to study on splitting tensile properties of rock after freeze-thaw cycles of rock mass in cold regions. The typical red sandstone in cold region was selected for testing, the freeze-thaw (F-T) cycle experiments with different numbers (0, 5, 10, 15, and 20 times) were performed on red sandstone specimens, and the effects of F-T cycle number on the P-wave velocity, dry density, and porosity of red sandstone were studied in detail. In addition, both the static and dynamic mechanical properties of red sandstone specimens after different F-T cycles were tested by using rock testing machine and ø50 mm split Hopkinson bar system, and the influence of F-T cycle number on the static and dynamic strength, deformation, and failure mode of red sandstone was systematically analyzed. F-T damage degree of red sandstone was defined based on the variation in P-wave velocity. Results show that with the increase of F-T number, the internal cracks of red sandstone continuously expand, bonding between mineral particles gradually decreases. Both the P-wave velocity and dry density of specimens gradually decrease, while the porosity and damage degree gradually increase. The static and dynamic splitting tensile strengths of red sandstone specimens gradually decrease with the increase of F-T number, while the time needed to reach the peak stress gradually increases. After 20 F-T cycles, the static and dynamic splitting strengths of red sandstone specimens decreased by 41.88% and 21.93%, respectively. Under the same F-T cycle number, the dynamic splitting strength of red sandstone specimens is increased by 2～3.5 times compared to the specimen under static loading. Under the static splitting condition, the red sandstone specimen exhibits the central splitting failure mode. However, an obvious crushed region at both ends of specimens was observed under dynamic loading. Additionally, with the increase of F-T number, the crushed area increases gradually, while the size of fragments gradually decreases. The damage degree of red sandstone increases logarithmically with the increase of F-T number.