Analysis of fracture toughness deterioration and instability model of dangerous rock masses under freeze–thaw cycles

The instability of dangerous rock masses is primarily caused by the stress intensity factor at the primary structural plane exceeding the fracture toughness of the rock bridge section, which results in the propagation of fractures. Additionally, in cold regions, the fracture toughness of these rock masses gradually decreases due to freeze–thaw cycles. Initially, considering the deterioration of type I and type II fracture toughness in the rock bridge section and the frost heaving force between structural planes, an assessment model for the stability of dangerous rock mass under freeze–thaw cycles is established. Secondly, utilizing the theory of circular hole expansion, along with the Mohr-Coulomb yield criterion and maximum tensile stress criterion, a model is constructed to simulate the degradation of type I and type II fracture toughness in rock bridge segments under the influence of freeze–thaw cycles. The validity of this model was subsequently verified through experimental validation. Finally, through engineering case studies, the degradation pattern of the stability of dangerous rock formations under the action of freeze–thaw cycles was analyzed. The study reveals that the decreasing stability of dangerous rock mass under freeze–thaw conditions is intricately linked to the internal friction angle, elastic modulus, and initial tensile strength of the rocks. Notably, the long-term stability of hard and coarsely textured dangerous rock mass under such conditions generally improves. Conversely, the tensile strength of the rock bridge segment elevates, which is beneficial for the long-term stability of the rock mass. When the residual debris ratio exceeds 0.25, the instability of the rock mass deteriorates more modestly. To maintain long-term stability, managing debris loss or injecting fillers into the pores can be effective strategies.