Abstract: To investigate the instability and failure of deep geological structural rocks under disturbed stress, which reduces the stability of surrounding rocks, we conducted a granite failure experiment involving real-time high-temperature biaxial cyclic loading and unloading at 250 ℃. This study examines the mechanical damage, energy evolution, and acoustic emission (AE) signal characteristics of granite subjected to cyclic loading and unloading with equal amplitude. The results are as follows: (1) As the stress level of cyclic loading and unloading disturbances increases, both the elastic modulus and irreversible strain of granite show an upward trend under varying lateral stresses. When the lateral stresses are 20, 40, 60 MPa, and 80 MPa, the elastic modulus increases by 7.73, 9.07, 10.23 and 9.87 GPa, respectively, while the irreversible strain increases by 1.2×10⁻³, 0.2×10⁻³, 0.4×10⁻³, and 0.5×10⁻³, respectively. The energy of the rock specimens exhibits a nonlinear growth trend, accompanied by a decrease in the proportion of dissipated energy. Specifically, at lateral stresses of 20, 40, 60 and 80 MPa, the proportion of dissipated energy decreases by 16.7%, 14.8%, 13.9%, and 11.9%, respectively, indicating that most of the input energy is stored as elastic energy. (2) The peak strength of granite increases with increasing lateral stress. At lateral stresses of 20, 40, 60, and 80 MPa, the corresponding peak strengths are 230.24, 263.81, 272.42, and 297.21 MPa, respectively. The elastic modulus of the rock also increases from 14.9 GPa to 15.8 GPa accordingly. Meanwhile, the irreversible strain decreases from approximately 3.3×10⁻³ to about 1.4×10⁻³. Regarding energy, the proportion of dissipated energy within the same loading interval decreases by 2.0% to 7.5%. (3) As confining pressure increases, the AE ringing counts significantly decrease, with peak counts of 29 383, 28 467, 17 539, and 9 436, respectively, and the frequency of AE ringing counts also declines. Under the same confining pressure, as cyclic loading and unloading progress, there is a sharp increase in AE ringing counts at failure. The b-value initially increases and then decreases, reaching its lowest value at failure, typically ranging between 4 and 7. The cumulative AE energy increases, with rapid growth occurring near failure. This research offers valuable insights into the mechanical properties and damage behaviors of deep geological structural rocks.

Key words: biaxial stress state, cyclic loading and unloading, real-time high temperature, damage characteristics, acoustic emission characteristics