真三轴压缩下碎裂花岗岩的软化特征

[Objective] This study aims to investigate the mechanical softening behavior of cataclastic granite under different in-situ stress conditions through true triaxial compression tests, thereby providing an experimental basis and theoretical references for the safe construction and long-term stability assessment of deep soft rock engineering. [Methods] Using the self-developed TAXW-5000 multi-field coupled true triaxial simulation system, true triaxial compression tests on cataclastic granite under different minimum principal stresses (σ 3) were conducted for the first time. The effects of the minimum principal stress on the mechanical response, post-peak softening behavior, and shear-dilation characteristics were systematically analyzed.Furthermore, in combination with 3D-CT scanning technology, the internal crack structures of the failed specimens were extracted and reconstructed, revealing the spatial distribution characteristics of the cracks. The damage evolution patterns of cataclastic granite under different in-situ stress environments were discussed. [Results] As the minimum principal stress (σ 3) increased from 1 MPa to 10 MPa, the peak stress of the cataclastic granite rose from 48.98 MPa to 80.42 MPa, and the residual stress increased from 27.17 MPa to 75.67 MPa. Meanwhile, the softening modulus decreased from 25.67 GPa to 4.81 GPa. During the softening stage, the shear-dilation coefficient decreased from 1.37 to 0.21 with increasing σ 3. In the residual stage, the shear-dilation coefficient first increased and then decreased with higher σ 3, reaching a maximum value of 1.21 at σ 3=5 MPa. CT scanning results indicated that a lower σ 3 led to a greater number and larger apertures of internal cracks in the failed specimens. The damage factor, calculated based on crack statistics, decreased from 0.29 to 0.12 as σ 3 increased from 1 MPa to 10 MPa. [Conclusion] With an increase in the minimum principal stress (σ 3), the softening modulus of cataclastic granite shows a negative correlation with σ 3. The shear-dilation coefficient in the residual stage is relatively high overall and exhibits a trend of first increasing and then decreasing with rising σ 3. In contrast, the shear-dilation coefficient in the softening stage decreases significantly, indicating a transition in the rock deformation mechanism from brittle to ductile failure. A higher σ 3 environment leads to more pronounced softening behavior in cataclastic granite, resulting in a lower degree of crack development and lower damage levels after failure, thereby enhancing the overall engineering stability.