Study on damage evolution characteristics of sandstone with different saturations in freeze-thaw environment

Abstract

In order to explore the damage evolution law of sandstone with different saturations under freeze-thaw environment, through freeze-thaw cycle, CT scanning and uniaxial compression test, and combined with three-dimensional visualization software and fractal theory, the evolution processes of porosity, permeability, pore parameters, throatparameters, fractal dimension and macroscopic mechanical indexes of natural water-bearing, incompletely saturated and completely saturated sandstone samples during the freeze-thaw processare quantitatively analyzed. The results show thatthe degree of freeze-thaw damage of rock samples is determined by the water saturation during freeze-thaw. Specifically, the damage deterioration of the completely saturated sandstone is the most severewhile the damage degree of the natural water-bearing sandstone is the lowest. The meso-structure of the completely saturated sandstone is highly heterogeneous, and its porosity, permeability, pore parameters, throat parameters and fractal dimension all increase exponentially with increasing the freeze-thaw number. However, for thenatural water-bearing sandstone and the incompletely saturated sandstone, these parameters increase linearly with increasing the freeze-thaw number. The porosity and the permeability of the samples are positively correlated with the fractal dimension, and freeze-thaw damage mainlypresentsin producing small pores and increasing the length of the original throat. The strength and the elastic modulus of three kinds of saturated sandstone samples decrease linearly with increasing the freeze-thaw number. After 150 freeze-thaw times, the strength of the completely saturated sandstone decreases by 98.53%, which is respectively 1. 68 and 1. 26 times higher than that of the natural water-bearing sandstoneand the incompletely saturatedsandstone. The macroscopic mechanical strength is negatively correlated with the porosity and the fractal dimension, and the meso-structure of rock is the key to affect the macroscopic mechanical properties. The initial freeze-thaw load damage variable is the freeze-thaw damage variable under the corresponding freeze-thaw number. The damage evolution curve has obvious stage characteristics, and the damage variable increases from concave to convex and then to gentlein the process of loading. The research results will provide a theoretical basis for the scientific evaluation of the long-term stability of rock mass engineering under the freeze-thaw environment in cold regions.