Experimental study on dynamic tensile mechanical properties of sandstone under freeze-thaw cycles

The western region of China is greatly affected by the freezing-thaw cycle. After experiencing the freezing-thawing cycle, the internal temperature stress of rocks will cause structural damage of rocks, and the physical and mechanical properties of rocks will change significantly, which will further affect the safety and reliability of rock engineering. In order to study the effect of freezing-thaw cycles on dynamic tensile mechanical properties of rocks, sandstones in typical cold and frozen regions of Xinjiang were selected and dynamic Brazil disk test was carried out on samples with different freezing-thaw cycles (0, 5, 10, 15, 20 and 25 times) using SHPB test system. The fragmenting characteristics of macro and micro of samples were analyzed by SEM scanning and high-speed camera, and the mechanism of freezing-thawing cycle was discussed. The results show that the freeze-thaw cycle has a great influence on dynamic tensile strength of sandstone, and the sample structure is damaged and the mechanical properties are deteriorated after the freeze-thaw cycle. With the increase of freezing-thawing cycle times, the structural damage and mechanical properties of the samples deteriorate. The dynamic tensile strength gradually decreased with the increase of the number of freeze-thaw cycles, and the decrease range was about 50% after 25 cycles. Under the same number of freeze-thaw cycles, the dynamic tensile strength has obvious strain rate enhancement effect. The fracture characteristics of sandstone after different freeze-thaw cycles are obviously different, and exfoliation failure and granular crushing failure occur〖LM〗at low strain rate and high strain rate, respectively. From a microscopic point of view, freeze-thaw cycle mainly affects rock mineral particles, cementing materials and pore area, and weakens the bonding force between rock particles. At the same time, different forms of fracture cracks are generated inside the rock. The frost heaving force and pore water pressure caused by freezing-thawing cycle lead to damage inside the rock, resulting in a decrease in strength on a macroscopic scale.