Experimental Study on the Effect of Freeze-Thaw Cycles on the Dynamic Characteristics of Green Sandstone

Freeze-thaw cycles have a crucial impact on the properties of rock materials. In order to study the effect of freeze-thaw cycles on the physical and dynamic compressive strength characteristics of green sandstone, a dynamic uniaxial compression test was conducted on freeze-thaw cycled green sandstone of 0, 25, 50, 75, and 100 cycles under 55.98 ~151.84 s⁻¹ impact. It is found that with the increase of freeze-thaw cycles, the mass and P-wave velocity decreased, while the porosity and saturated water absorption increased. Green sandstone with over 50 freeze-thaw cycles had severe internal damage, and the saturation water absorption rate increase of green sandstone gradually decreased, and the number of crystal-piercing cracks and crack clusters increased. The number of freeze-thaw cycles and the strain rate had opposite effects on the dynamic compressive strength, while both the number of freeze-thaw cycles and the increase in strain rate increased the degree of sandstone fragmentation. The freeze-thaw damage factor was established by combining the longitudinal wave velocity and porosity and the dynamic compressive strength empirical equation, taking the freeze-thaw damage and the strain rate into account, was obtained. The strength attenuation models built on the P-wave velocity and porosity can reflect the degradation law of the dynamic compressive strength. The dynamic compressive strength decreases with the increase of the P-wave velocity and porosity.