Damage and Energy Evolution Characteristics of Granite under Triaxial Stress
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摘要: 为揭示不同围压下硬岩在破坏过程中的力学性质和能量演化规律，基于RMT-150B岩石力学试验系统对花岗岩试样进行不同围压条件下常规三轴压缩试验。研究结果表明：岩样的峰值应力和围压具有较强的线性关系，利用Mohr-Coulomb强度准则求出花岗岩的黏聚力为23.548 MPa，内摩擦角为57.629°。围压对花岗岩加载破坏过程中能量演化的影响显著，岩石的峰值能量、弹性应变能以及耗散能都随着围压的增大而增大，且两者呈线性增加关系。根据岩石的线性储能规律，提出了确定岩石应力阈值的方法。围压越大，起裂应力和扩容应力越大，且岩样起裂点处与扩容点处的能量也越大；当围压较低时，岩石破坏前储存的能量较少，破坏时能量释放速率低，岩样表现为典型低劈裂破坏；在高围压情况下，能量快速释放，岩样表现为剪切破坏。基于能量演化规律，提出了岩石损伤演化模型，得到了花岗岩的损伤变量D在不同围压下加载破坏过程中的演化规律。Abstract: In order to reveal the mechanical properties and energy evolution of hard rock under different confining pressures, conventional triaxial compression tests on granite samples under different confining pressures were carried out by the RMT-150B rock mechanics test system. The results showed that the peak stress of the rock sample had a strong linear relationship with the confining pressure. The cohesive force of the granite was 23.548 MPa and the internal friction angle was 57.629° using the Mohr-Coulomb strength criterion. The peak energy, elastic strain energy and dissipation energy of the rock all increased linearly with the increase of confining pressure. According to the linear energy storage law of the rock, a method to determine the rock threshold stress was proposed, the greater the confining pressure, the larger of cracking stress and expansion stress, the larger the energy at the initiation point and the expansion point of the rock sample. When the confining pressure is low, there existed less energy stored in the rock before failure, the energy release rate is low, and the rock sample shows typical splitting failure. Under high confining pressure, the energy gets released rapidly, and the rock sample shows shear failure. Besides, a rock damage evolution model was proposed based on the law of energy evolution, and the law of evolution of damage variable D on the granite was obtained during loading failure under different confining pressures.
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Key words:
- triaxial compression /
- mechanical properties /
- energy evolution /
- damage model; granite
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图 2 不同围压下花岗岩的应力-应变曲线
Figure 2. Stress-strain curves of granite underdifferent confining pressures
图 3 围压与峰值应力、应变的关系
Figure 3. Relationship of peak stress and strain with confining pressure
图 4 不同围压下花岗岩岩样的破坏特征
Figure 4. Failure characteristics of granite samples under different confining pressures
图 5 岩石压缩过程中Ud 和Ue 的关系
Figure 5. Relationship between Ud and Ue in rock failure process
图 6 不同围压下花岗岩的能量演化特征
Figure 6. Energy evolution characteristics of granite under different confining pressures
图 7 不同围压下的应力阈值及能量
Figure 7. Stress threshold and energy under different confining pressures
图 8 围压与峰值点处能量的关系
Figure 8. The relationship between confiningpressure and energy at peak point
图 9 不同围压下的花岗岩损伤曲线
Figure 9. Damage curves of granite underdifferent confining pressures
表 1 不同围压下花岗岩的力学性质参数
Table 1. Mechanical properties of granite under different confining pressures
Confining pressure/MPa Peak strain/10−3 Peak stress/MPa 0 4.603 141.784 5 5.408 241.736 10 5.988 293.816 15 6.852 336.105 20 7.757 391.337 
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表 2 不同围压下的应力阈值及能量
Table 2. Stress threshold and energy under different confining pressures
The point $\sigma $3/MPa $\sigma $ci/MPa $\sigma $cd/MPa U/MJ Ue/MJ Ud/MJ Initiation point 5 157.93 0.200 0.164 0.036 10 175.37 0.239 0.198 0.041 15 192.83 0.307 0.244 0.063 20 235.48 0.437 0.367 0.070 Expansion point 5 236.71 0.432 0.380 0.052 10 279.43 0.596 0.509 0.087 15 313.67 0.830 0.675 0.155 20 362.73 1.086 0.910 0.176
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表 3 不同围压下峰值点处的能量
Table 3. Energy at peak points under different confining pressures
Confining pressures/MPa U/MJ Ue/MJ Ud/MJ Ue·U −1 Ud·U −1 0 0.386 0.320 0.066 0.829 0.171 5 0.464 0.400 0.064 0.862 0.138 10 0.749 0.566 0.183 0.756 0.244 15 1.128 0.777 0.351 0.688 0.312 20 1.654 1.099 0.555 0.665 0.335
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