Experimental study on instability and failure mechanism of sandstone under freeze-thaw and load

Abstract

In order to study the influence of loading rate and freeze-thaw cycles on the mechanical properties of sandstones, uniaxial compression tests were conducted on sandstone samples subjected to various freeze-thaw cycles and loading rates. Both internal and external damages were monitored throughout the tests using an acoustic emission (AE) detection system and a high-speed camera system. The effects of loading rate and freeze-thaw cycle on the typical mechanical properties, failure modes, and AE characteristics of sandstone were analyzed. In addition, attenuation models were established for the strength indices of freeze-thaw affected sandstone under different loading rates. Based on the results of the analyses, the following main conclusions are drawn: With the increase in freeze-thaw cycles and the decrease in loading rate, the uniaxial compressive strength(UCS) and elastic modulus(E) of sandstone decrease and the ductility increases, whereas the attenuation constant λ decreases as the loading rate increases. Upon complete failure, the number of tensile cracks in the sandstone exceeds that of shear cracks. As the number of freeze-thaw cycles increases and the loading rate decreases, the proportion of shear cracks gradually increases. With the increase in the loading rate, sandstone damage is primarily due to tension, and with more freeze-thaw cycles, damage is mainly due to both tension and shear. When the internal cracks in sandstone start to extend, the AE events rate and b-value signals become active. The absence of low AE events rate and a sharp decline in AE b-value can serve as precursors for predicting instability and failure of sandstones subjected to varying loading rates and freeze-thaw cycles.