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真三轴压缩下碎裂花岗岩的软化特征
Softening Characteristics of Fractured Granite under True Triaxial Compression
探究地应力环境下碎裂花岗岩的软化特征对地下软岩工程的建设和服役具有重要的意义。通过自主研发的TAXW-5000多场耦合真三轴模拟系统开展了不同最小主应力条件下碎裂花岗岩的真三轴压缩试验,分析了不同最小主应力对碎裂花岗岩的力学特性和软化扩容特征的影响。研究结果表明:最小主应力从1 MPa增大至10 MPa,碎裂花岗岩的峰值应力从48.98 MPa增加至80.42 MPa,残余应力从27.17 MPa增加至75.67 MPa,且峰值应力和残余应力均与最小主应力满足线性相关关系;碎裂花岗岩的软化模量与最小主应力之间满足负相关关系。随着最小主应力的增大,碎裂花岗岩软化阶段的剪胀扩容系数减小,碎裂花岗岩的变形特征由脆性破坏向延性破坏转变。而残余阶段剪胀扩容系数整体较大,且随着最小主应力的增大,表现出先增大后减小的变化趋势。研究结果将为地下软岩工程的建设和服役安全提供重要的试验和理论支撑。
[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 (σ3) 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 (σ3) 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 σ3. In the residual stage, the shear-dilation coefficient first increased and then decreased with higher σ3, reaching a maximum value of 1.21 at σ3=5 MPa. CT scanning results indicated that a lower σ3 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 σ3 increased from 1 MPa to 10 MPa. [Conclusion] With an increase in the minimum principal stress (σ3), the softening modulus of cataclastic granite shows a negative correlation with σ3. The shear-dilation coefficient in the residual stage is relatively high overall and exhibits a trend of first increasing and then decreasing with rising σ3. 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 σ3 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.
true triaxial tests / cataclastic granite / softening and dilatancy / principal stress
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