Mechanical Properties and Acoustic Emission Characteristics of Granite under Different Unloading Rates of Confining Pressures
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摘要: 为了研究不同卸围压速率下花岗岩的力学性质，利用RMT-150B岩石力学试验系统对花岗岩试样进行恒轴压卸围压应力路径试验。试验结果表明：相同的初始围压下，随着卸围压速率增大，岩样的延性减小，表现为脆性破坏。卸围压速率越大，卸围压阶段的应变率越高，但总变形量小；当卸围压的速率相同时，初始围压越高，卸围压阶段岩样的应变率和总变形量越大。采用Mogi-Coulomb强度准则对试验结果进行拟合，结果显示：卸围压速率对花岗岩的黏聚力有劣化作用，对岩石的内摩擦角有强化作用；卸围压速率越小，振铃计数的活跃期越长，表明在低卸围压速率下，花岗岩岩样内部损伤发展缓慢且完全。Abstract: In order to study the mechanical properties of granite under different unloading confining pressure rates, tests for the granite unloading confining pressure stress path under constant axial pressure were conducted via RMT-150B rock mechanics test system. The results show that: under the same initial confining pressure, the ductility of rock sample gets decreased with the increase of unloading confining pressure rate, which is characterized by brittle failure. The higher the unloading confining pressure rate is, the greater the strain rate is in the duration of confining pressure unloading, but the total deformation keeps small. Under the same unloading rate, the higher the initial confining pressure is, the greater the strain rate as well as the total deformation is. Then using Mogi-Coulomb intensity criterion to fit the test results, it is concluded that the unloading confining pressure rate degrades the cohesion of granite and strengthens the internal friction angle of rock; the smaller the unloading confining pressure rate is, the longer the active period of ringing count is, indicating a slow but complete development of the internal damage in granite samples under low confining pressure release rate.
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图 3 不同卸围压速率下花岗岩的应力-应变曲线
Figure 3. Stress-strain curves of granite under different release confining pressure rates
图 4 卸围压试验中花岗岩的破坏形式
Figure 4. Failure patterns of granite in unloading confining pressure tests
图 5 不同初始围压、卸荷速率下的应变率变化
Figure 5. Variation of strain rate under different initial confining pressure and unloading rate
图 6 花岗岩峰值强度-围压线性拟合结果
Figure 6. Relationship between peak strengthand confining pressure for granite
图 8 不同卸围压速率下花岗岩的黏聚力和摩擦角
Figure 8. Cohesions and friction angles of granite under different unloading rates
图 9 不同围压和卸荷速率下花岗岩的声发射特性
Figure 9. Acoustic emission characteristics of granite under different confining pressure and confining pressure unloading rate
表 1 两种强度准则的线性拟合结果
Table 1. Linear fitting results of two strength criteria
Condition v/（MPa·s−1） Mohr-Coulomb criteria Mogi-Coulomb criteria $\xi $ $\sigma\rm{_c }$ R2 a b R2 Triaxial compression 8.749 186.48 0.900 47.13 0.54 0.977 Unloading confining pressure 0.002 7.771 135.54 0.848 13.01 0.74 0.990 0.02 6.581 147.51 0.943 17.71 0.80 0.995 0.2 5.641 170.58 0.966 24.17 0.66 0.999 
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