An experimental study on the shear strength and shear fracture evolution of freeze–thaw granite containing rock bridges based on digital image correlation

Abstract

Rock bridges play a critical role in controlling the overall stability of locked rock slopes. In order to explore the influence of freeze–thaw cycles on the shear characteristics of locked rock masses, an experimental study was conducted to analyze the deformation, crack initiation, and propagation patterns of freeze–thaw granite containing rock bridges under compressive-shear conditions. Utilizing digital image correlation (DIC) technology, direct shear tests of specimens that contained rock bridges were conducted on the DTW_1000 variable-frequency and variable-amplitude rock dynamic shear testing system. The results indicate that an increase in the number of freeze–thaw cycles (FT = 0 ~ 60) has a significant impact on the shear strength of rocks. Under constant normal stress, after 60 freeze–thaw cycles, the shear stress decreases by 22.37%, the macroscopic failure of the rock transitions from brittle to ductile, and the plastic deformation zone at the end face gradually increases, making shear failure more prone to occur. The DIC two-dimensional shear strain E_xy evolution contour map showed that under the action of horizontal stress, an uneven tensile stress field is formed at the upper and lower ends, causing tensile cracking at the tip of the rock bridge, ultimately leading to the failure of the specimen. With an increase in the number of freeze–thaw cycles, the damage parameters for θ, K_IIc, σ_r, and σ_θ decrease, and the crack propagation angle reduces from 41.3° to 24.5°. The image of crack propagation angle obtained by DIC visually shows the degree of freeze–thaw damage to the rock, and the fundamental reason is the reduction of internal friction angle and cohesion in the rock. Freeze–thaw aggravates the damage of rock bridge, which is the main reason why the shear stress deteriorates with the increase of freeze–thaw cycles. The damage to rock bridges caused by freeze–thaw cycles can lead to geological hazards such as collapses and landslides. In-depth research under freeze–thaw conditions on the crack initiation, propagation, and shear-through behavior of rock masses that contain rock bridges is crucial for understanding the deformation and fracturing mechanisms of such masses.