Failure characteristics of heated granite under different minor principal stresses: an experimental study

High temperature is a crucial external environmental factor that significantly affects rock failure. This study involved conducting true-triaxial compressive tests on heated granite specimens to examine the influence of heat treatment on granite failure under different minor principal stresses (σ₃ = 0.5, 5, and 15 MPa). The specimens were heated to the following maximum temperatures: 25 ℃ (without heat treatment), 100 ℃, 300 ℃, 500 ℃, and 600 ℃. The experimental results indicate that specimen strength first increased and then decreased as the maximum heating temperature increased from 25 ℃ to 600 ℃, reaching peak strength at 300 ℃, indicating an obvious effect of heat treatment on rock strength. High σ₃ enhanced the effect of heat treatment on rock strength. Additionally, the pre-peak strains indicated an obvious transition in specimen deformation characteristics from brittleness to ductility as the maximum heating temperature increased to about 500℃ under σ₃ = 0.5 MPa. However, this transition became less clear with increasing σ₃, indicating that σ₃ masks the effect of heating on rock deformation. Furthermore, the failure severity of the heated specimen first increased and then decreased as the maximum heating temperature increased. All tested specimens exhibited a mixed tensile-shear failure mode. When the maximum heating temperature was low, the failure mode of the tested specimens changed from mode I to mode II as σ₃ increased from 0.5 MPa to 15 MPa. When the maximum heating temperature was high, the failure mode changed from mode II to mode III with increasing σ₃.