Effect of freeze-thaw cycle on physical and mechanical properties and damage characteristics of sandstone.

Rock deterioration under freeze-thaw cycles is a concern for in-service tunnel in cold regions. Previous studies focused on the change of rock mechanical properties under unidirectional stress, but the natural rock mass is under three dimensional stresses. This paper investigates influences of the number of freeze-thaw cycle on sandstone under low confining pressure. Twelve sandstone samples were tested subjected to triaxial compression. Additionally, the damage characteristics of sandstone internal microstructure were obtained by using acoustic emission (AE) and mercury intrusion porosimetry. Results indicated that the mechanical properties of sandstone were significantly reduced by freeze-thaw effect. Sandstone' peak strength and elastic modulus were 7.28-37.96% and 6.38-40.87% less than for the control, respectively. The proportion of super-large pore and large pore in sandstone increased by 19.53-81.19%. We attributed the reduced sandstone' mechanical properties to the degenerated sandstone microstructure, which, in turn, was associated with increased sandstone macropores. The macroscopic failure pattern of sandstone changed from splitting failure to shear failure with an increasing of freeze-thaw cycles. Moreover, the activity of AE signal increased at each stage, and the cumulative ringing count also showed upward trend with the increase of freeze-thaw number.