Objective To determine the deformation and failure mechanisms of fractured rock masses with rock bridges in alpine regions, this study conducted mechanical property tests on rock samples with varying lengths of rock bridges subjected to cyclic freezing and thawing.

Methods Through experiments, this study summarized the characteristics of the static strength deterioration of rock masses under the combined effects of different numbers of freezing and thawing cycles and varying rock bridge lengths. By combining acoustic emission signal monitoring and scanning electron microscopy, this study thoroughly explored both the evolutionary characteristics of fractures and rock rupture modes. Accordingly, it revealed the macroscopic and microscopic failure mechanisms of rock masses with varying lengths of rock bridges under cyclic freezing and thawing.

Results  The results indicate that with an increase in the number of freezing and thawing cycles, the rock sample with a shorter rock bridge exhibited greater loss rates of both mass and P-wave velocity. As the number rose, the peak strengths and moduli of elasticity of the rock samples gradually decreased, with their deterioration rates significantly decreasing. In the case of the same number of freezing and thawing cycles, a smaller distance between the bottom of a rock sample and fractures in the lower part of the rock bridge of the sample led to a lower overall rock mass strength. The peak stresses of rock samples with different lengths of rock bridges decreased in the order of the intact sample, and samples with rock bridge lengths of 50 mm, 60 mm, and 40 mm sequentially. Acoustic emission tests demonstrated that the sample with a 50-mm-long rock bridge exhibited the highest cumulative ringing count, while that with a 40-mm-long rock bridge showed the lowest count. The ringing count of the rock samples showed a positive correlation with peak stress but a negative correlation with the number of freezing and thawing cycles. The b-value in the acoustic emission tests fluctuated generally. Cyclic freezing and thawing caused the b-value to decline earlier, corresponding to the formation of large fractures in rocks. Macroscopically, the rock samples showed a more random microcrack direction distribution at the rock bridge tips after cyclic freezing and thawing. Consequently, penetration failure of the rock bridges occurred more rarely, with the failure mode shifting from single failure to tensile-shear hybrid failure. Microscopically, the damage mode evolved from cement damage to the breakage of mineral grains, with the fragmentation zone expanding progressively. These findings indicated that with an increase in the number of freezing and thawing cycles, the tightness of rock sample structures decreased significantly. As a result, intergranular fractures became interconnected to form networks and penetrated, leading to the significant denudation of cemented minerals and causing a systematic loss of inter-particle bonding force.

Conclusions Adjusting the rock bridge length plays a key role in enhancing rock masses’ resistance to freezing and thawing in alpine regions, with the optimal rock bridge length contributing to effectively reduced ranges of stress concentration zones at fracture ends and slow deterioration caused by cyclic freezing and thawing. In engineering practices, the rock bridge length should be appropriately adjusted to achieve a balance between freeze resistance and mechanical stability. Furthermore, it is necessary to enhance the monitoring of fracture tips to restrict the rapid degradation induced by stress concentration.