Creep acoustic emission characteristics and failure precursor identification of double-fissured red sandstone under freeze–thaw action

Rock masses in cold regions deteriorate due to frost heave caused by fissure water, posing risks to engineering projects. This study investigates the long-term mechanical behavior of fully saturated fissured red sandstone under freeze-thaw conditions. Creep acoustic emission (AE) experiments were conducted to explore how freeze-thaw cycles and fissure dip angles influence rock creep and AE characteristics. Four freeze-thaw cycle levels (0, 30, 60, and 90) and three double-fissure orientations (15°-15°, 15°-75°, and 75°-75°) were examined in this study. Results show that: (1) Increasing freeze-thaw cycles lead to greater instantaneous and creep strains, higher AE signal amplitudes, exponential growth in AE energy rates, and faster b-value fluctuations. (2) With larger fissure dip angles, the instantaneous and creep strains significantly increase, while the amplitude density, intensity, and AE energy rates decrease. b-value fluctuations also slow down. (3) Abrupt b-value changes can predict freeze-thaw-induced rock failure. For intact samples subjected to 90 freeze-thaw cycles, intact non-freeze-thaw samples, and fissured non-freeze-thaw samples, b-value mutations occurred 12.96 s, 35.28 s, and 48.24 s earlier, respectively. These findings highlight b-value changes as an early indicator of freeze-thaw damage and provide theoretical insights into the creep failure of fissured rock masses under such conditions, aiding in the design and safety of cold-region engineering.