Test Study on True-Triaxial Loading and Unloading for Marble with Unloaded Single Face
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摘要: 为了准确地评价巷（隧）道开挖面附近围岩的稳定性，采用真三轴卸荷扰动岩石测试系统对大理岩岩样进行第三主应力单面卸荷加、卸载试验研究. 通过高应力巷（隧）道开挖围岩失稳机理分析，采用不同应力加卸路径模拟能量积聚型和应力集中型两种物理工程破坏模型，进一步分析两种破坏模型的应力-应变曲线规律、破坏特征和强度特征. 研究结果表明：随着卸荷面应力的减小出现扩容现象，主要破坏面在临空面附近，随着轴压的升高，劈裂破坏范围增大，卸荷临界值也增大；随着围压增高，屈服点和峰值点增大，并且屈服点和峰值之间的曲线斜率较为平缓，破坏由局部张拉-劈裂-剪切复合性破坏发展成整体劈裂破坏；同围压条件下卸荷破坏强度是加载破坏强度的80%，岩体卸荷比加载更容易破坏，进而修正了广义Hoek-Brown强度准则.
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关键词:
- 真三轴试验 /
- 单面卸荷 /
- Hoek-Brown准则 /
- 破坏特征
Abstract: To accurately evaluate rock stability around the excavation face of roadway（tunnel）, a true-triaxial unloading disturbance testing system is applied in the loading and unloading tests of marble samples, where single-face was unloaded in the direction of the minimum principal stress. Through the analysis on instability mechanism of rock around roadway excavation face with high geostress, two kinds of failure modes, including energy accumulation failure and stress concentration failure, were simulated in different loading and unloading paths. Then, stress-strain curves, and failure and strength characteristics were further analyzed. The results indicate that there is dilatancy when the stress on unloading surface decreases; the main failure surface is near the free face; moreover, with the increase of the axial load, the splitting failure area extends and the critical unloading value increases. With the increase of the confining pressure, the stress peaks and yields increase, and the curve slope between the yield and peak is reduced. The composite failure mode with local tension-splitting-shear failures develops into the overall splitting failure. Under the same confining pressure, the unloading failure strength is 80% of the loading failure strength, and the marble sample in unloading is more likely to fail than in loading. The Hock-Brown criterion is modified using the calculated fracture strength value. -
图 5 加、卸荷应力-应变曲线对比
Figure 5. Stress-strain curves under loading and unloading conditions
图 6 能量积聚型单面卸荷破坏应力-应变曲线
Figure 6. Stress-strain curves of energy accumulation failure with single-face unloading
图 7 轴向应力与卸荷面临界值拟合曲线
Figure 7. Fitting curve for the critical values with single-face unloading vs. axial stress
图 8 单面卸荷应力集中型破坏应力-应变曲线
Figure 8. Stress-strain curves of stress concentration failure model with single-face unloading
图 10 能量积聚型单面卸荷宏观破坏示意
Figure 10. Energy accumulation failure of marble samples with single-face unloading
图 11 单面卸荷应力集中型宏观破坏示意
Figure 11. Stress concentration failure of marble samples with single-face unloading
图 12 修正Hoek-Brown强度准则验证试验
Figure 12. Validation of modified Hoek-Brown strength criterion
表 1 初始应力值
Table 1. Initial stresses
岩样编号 $ {\sigma _1}$ $ {\sigma _2}$ $ {\sigma _3}$ 1# 0 0 0 2# 140.0 20.0 10.0 3# 160.0 20.0 10.0 4# 180.0 20.0 10.0 5# 200.0 20.0 10.0 6# 220.0 20.0 10.0 7# 50.0 5.0 2.5 8# 50.0 10.0 5.0 9# 50.0 20.0 10.0 10# 50.0 30.0 20.0 
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表 2 第三主应力单面卸荷临界值
Table 2. Critical values of minimum principal stress under single-face unloading condition
轴压 卸荷临界值 破坏程度 140 0 不破坏 160 0.38 破坏 180 0.74 破坏 200 1.62 剧烈破坏 220 2.99 剧烈破坏
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