Mechanical properties and strain localization characteristics of gneiss under freeze-thaw cycles

In high-altitude or cold regions, the deterioration effect of freeze-thaw (F-T) weathering on rocks is considerable. This study investigated the mechanical properties, microstructures, failure modes, and apparent strain fields of gneiss samples subjected to different F-T cycles under uniaxial compression. Combined with the convolution principle, the edges of strain localization were accurately detected, and further three factors (spatial localization factor, numerical localization factor, and damage localization factor) were proposed to characterize the strain localization characteristics and the effect of F-T cycles on them. Results show that the uniaxial compressive strength and elastic modulus decrease linearly with the increase of F-T cycles, and the failure mode transforms from tensile failure to tensile-shear composite failure and to shear failure. The reason for these changes is the deterioration effect of F-T cycles on the rock microstructures. Under uniaxial compression, the strain localization bands develop progressively accompanied by the changes in the spatial and numerical characteristics. Moreover, the development process can be divided into three stages: stable localization development stage, accelerated localization development stage, and post-peak localization development stage. In addition, both the stress and stress level of localization initiation decrease linearly with increasing F-T cycles. At the peak stress, the spatial localization factor increases roughly, while the numerical localization factor and damage localization factor decrease. These findings indicate that the action of F-T cycles exerts a promoting effect on the initiation and development of strain localization of rocks.