Study on Failure Mode and Energy Evolution of Fractured Rock Body under Triaxial Compression
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摘要: 为研究不同围压条件下含不同长度单裂隙岩体的裂纹扩展特征和能量演化规律,基于室内三轴压缩试验结果标定细观参数,开展了PFC2D颗粒流数值模拟试验。结果表明:拉伸裂纹先于剪切裂纹产生,两者呈指数增长,裂隙长度减小和围压增大使拉伸裂纹和剪切裂纹快速增长时间滞后;最终破坏时,随裂隙长度增加,拉伸裂纹和剪切裂纹减少。应力集中于裂隙两端,裂纹周围存在应力集中现象。相同围压下,裂隙长度增加,岩样破坏时块体数减少。岩体破坏本质为能量储存、耗散与释放的过程,在加载过程中,岩体能量转化被分为4个阶段。裂隙长度增加削弱岩样储存应变能的能力,总能量减少,围压增强岩样储存应变能的能力。岩样破坏时,耗散能大于应变能,随裂隙增长,耗散能减少。Abstract: To study the crack extension characteristics and energy evolution law of the rock body with different lengths of single fissure under different confining pressures, the mesoscopic parameters were calibrated by use of the indoor triaxial compression test, and the numerical simulation test of PFC2D particle flow was carried out. The results show that tensile cracks are generated before shear cracks, and both of them grow exponentially; the decrease of the fissure length and the increase of the confining pressure restrain the rapid growth of tensile and shear cracks; when the final failure occurs, the tensile and shear cracks decrease with the increase of the fissure length. The stress is concentrated at both ends of the crack, and there is stress concentration around the crack. Under the same confining pressure, the number of failure blocks of the rock sample decreases with the increment of fissure length. The nature of rock failure is the process of energy storage, dissipation and release, and the rock energy transformation is divided into four stages during the loading process. The increase in fissure length weakens the ability of the rock samples to store strain energy, the total energy decreases, and the confining pressure enhances the ability of the rock samples to store strain energy. The dissipated energy is greater than the strain energy when the rock sample fails, and the dissipated energy decreases with the fissure growth.
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表 1 岩石PFC模型细观参数
Table 1. Mesoscopic parameters of the rock PFC model
Minimum radius of particles/mm Ratio of maximum to minimum of radius Density of the particle/
(kg·m−3)Friction coefficient Bond friction angle/(º) 0.3 1.5 2 950 0.17 40 Parallel bonding stiffness ratio Particle stiffness ratio Effective modulus of bonding/GPa Tangential bond strength/MPa Normal bond strength/MPa 1.1 1.1 11 76.6 69.6 Method Deviatoric stress/MPa Elastic modulus/MPa Indoor test[16] 144.782 17.147 Numerical simulation 144.670 17.109 Error/% 0.077 0.222 表 3 不同裂隙长度的岩样在不同围压下的接触力链演化过程
Table 3. Evolution of contact force chainof rock samples under different confining pressures and fissure lengths
L/mm Confining pressure/MPa Pre-peak period Peak value Post-peak period 0 5.0 10.0 5 5.0 10.0 10 5.0 10.0 表 4 不同裂隙长度岩样的峰值点能量指标
Table 4. Indexes of peak point energy of rock samples with different fissure lengths
L/mm Confining pressure/MPa Total energy/kJ Dissipated energy Energy/kJ Proportion/% 0 2.5 288.67 9.54 3.30 5.0 324.79 10.41 3.21 10.0 415.48 14.47 3.48 15.0 474.29 21.31 4.49 5 2.5 248.58 8.24 3.31 5.0 281.97 9.11 3.23 10.0 348.54 12.51 3.59 15.0 355.56 12.34 3.47 10 2.5 172.37 4.89 2.84 5.0 205.55 7.32 3.56 10.0 279.90 9.16 3.27 15.0 293.19 10.24 3.49 15 2.5 153.98 5.86 3.8 5.0 169.91 5.02 2.95 10.0 215.02 7.95 3.70 15.0 240.84 10.34 4.29 -
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