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ESTIMATION AND VERIFICATION OF UNIAXIAL TENSILE STRENGTH OF SATURATED HARD ROCKS
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摘要: 因试样制备、试验操作等限制，获得饱和岩石的直接拉伸强度较为困难。为对饱和硬岩的直接拉伸强度进行合理估算并验证其可靠性，同时分析水对估算误差的影响，设计完成了干燥、饱和状态下两种硬岩的单轴压缩和直接拉伸声发射试验。基于Griffith理论和Hoek-Brown(H-B)强度准则，通过裂纹体积应变法确定岩石起裂应力，估算饱和硬岩的直接拉伸强度和H-B强度参数mi。结合声发射波形信号频谱特性，分析两者估算结果的准确性。结果表明，基于Griffith准则并采用起裂应力估算饱和硬岩的直接拉伸强度是一种较可靠的方法。对于干燥硬岩，该方法确定的直接拉伸强度估算值比试验值偏小。饱和硬岩直接拉伸强度估算值与试验值基本接近，这是因为硬岩饱和后，延性和蠕变趋向增强，并发生更多的微观拉破裂。饱和硬岩的mi值增大与增多的微观拉破裂有关，mi值变化可用于描述饱和硬岩的软化程度。基于Griffith准则并采用起裂应力估算的岩石直接拉伸强度和H-B强度参数mi可用于岩体工程的早期设计。
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关键词:
- 岩石力学 /
- 饱和硬岩 /
- 直接拉伸强度 /
- 起裂应力 /
- Griffith理论
Abstract: The uniaxial tensile strength(UTS) of saturated rocks is not easy to obtain because of the difficulty in specimen preparation and test execution. To estimate the saturated rocks' UTS and analyze the water effects on its accuracy,we conducted a series of uniaxial compression and direct tension tests of two hard rocks,coupled with acoustic emission(AE)monitoring. Based on the Griffith theory and Hoek-Brown(H-B)criterion,crack initiation stress determined by crack volumetric strain curve was utilized to evaluate the UTS and H-B strength parameter mi. The accuracy of estimation of these two parameters was analyzed by the spectrum characteristics of AE waveforms. Results show that,the method of crack initiation stress based on Griffith criterion is reliable to estimate the saturated hard rocks' UTS. The estimated values of dry hard rocks' UTS are smaller than those of experimental values. In comparison,the estimated saturated rocks' UTS is closer to the experimental value. This is mainly because the ductility and creep of hard rocks tend to increase after saturation,and more micro-tensile failures occur inside the rocks. The increase in mi of saturated hard rocks is related to the growing micro-tensile failures. Moreover,the mi can be used to describe the degree of the water-weakening effect. The estimation of rock UTS andmi based on Griffith's theory and crack initiation stress can be applied in the early design of rock mass engineering practice. -
图 1 大岗山水电站引水隧洞工程岩体拉伸破坏
Figure 1. Tensile failure of rock mass in diversion tunnel of Dagangshan station
图 2 不同方法确定起裂应力示意图
Figure 2. Diagram of crack initiation stress identification by different methods
图 3 岩石矿物成分分析与加工后试样
Figure 3. Mineral composition of marble and samples after processed
图 4 单轴压缩试样加载示意图
a. 位移传感器与探头布置；b. 声发射探头分布
Figure 4. Schematic diagram of sample loading for uniaxial compression tests
图 5 直接拉伸试验装置与试样加载示意图
Figure 5. Diagram of devices and sample loading for direct tensile tests
图 6 干燥、饱和岩石单轴压缩与直接拉伸强度
a. 单轴抗压强度UCS；b. 直接拉伸强度UTS
Figure 6. Uniaxial compressive strength and direct tensile strength of dry and saturated rocks
图 7 典型大理岩试样裂纹体积应变曲线
a. 干燥大理岩试样CMD1；b. 饱和大理岩试样CMS1
Figure 7. Crack volumetric strain curve of typical marble specimen
图 8 典型灰岩试样裂纹体积应变曲线
a. 干燥灰岩试样CLD1；b. 饱和灰岩试样CLS1
Figure 8. Crack volumetric strain curve of typical limestone specimen
图 9 两种岩石的拉伸强度估算值与试验均值对比
a. 大理岩；b. 灰岩
Figure 9. Comparison of estimated and experimental mean tensile strength
图 10 典型声发射信号时域和频谱图
a. 时域图；b. 频域图
Figure 10. The time and domain spectrum of one typical AE waveform
图 11 压缩条件下干燥、饱和硬岩声发射高低主频占比
Figure 11. The proportion of high and low dominant frequency of AE waveforms for dry and saturated hard rocks under compression
表 1 试样基本物理力学参数
Table 1. Basic physical parameters of samples
岩石类型 组别 编号 天然密度/kg·m-3 孔隙度/% 纵波波速/m·s-1 大理岩 1 CMD1~6 2.68 (±0.06) 6.31 (±0.18) 4236 (±27.81) 2 CMS1~6 3 TMD1~6 4 TMS1~6 灰岩 1 CLD1~6 2.63 (±0.12) 4.46 (±0.11) 3352 (±21.38) 2 CLS1~6 3 TLD1~6 4 TLS1~6 括号内表示参数标准差。试样编号ABCn中，A代表试验类别，其中C表示压缩试验，T表示直接拉伸试验；B代表岩石类型，其中M表示大理岩，L表示灰岩；C代表试样状态，其中D代表干燥试样，S代表饱和试样；n表示第n个样本。 
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表 2 大理岩抗拉强度σt和强度参数mi估算值统计
Table 2. Practical estimate of tensile strength σt and strength parameter mi of marble
岩石类型 试样编号 状态 σci/MPa σci/σc/% σt估算/MPa σt估算误差/% mi估算 大理岩 CMD-1 干燥 17.30 25.34 2.16 12.80 32 CMD-2 19.38 30.08 2.42 2.32 27 CMD-3 18.50 28.32 2.31 6.75 28 CMD-4 17.58 26.71 2.20 11.39 30 CMD-5 19.06 27.48 2.38 3.93 29 CMD-6 17.53 27.35 2.19 11.64 29 均值 18.23 27.55 2.28 8.14 29 CMS-1 饱和 13.45 25.56 1.68 3.93 31 CMS-2 13.78 25.92 1.72 1.57 31 CMS-3 13.26 25.97 1.66 5.31 31 CMS-4 12.96 24.34 1.62 7.43 33 CMS-5 12.91 25.20 1.61 7.79 32 CMS-6 13.45 24.54 1.68 3.93 33 均值 13.30 25.26 1.66 4.01 32 灰岩 CLD-1 干燥 48.76 36.88 6.10 11.28 22 CLD-2 52.91 38.51 6.61 3.73 21 CLD-3 41.63 31.90 5.20 24.25 25 CLD-4 46.74 35.64 5.84 14.96 22 CLD-5 47.99 35.34 6.00 12.68 23 CLD-6 49.81 38.16 6.23 9.37 21 均值 47.97 36.07 6.00 12.71 22 CLS-1 饱和 32.47 32.49 4.06 6.05 25 CLS-2 31.82 31.37 3.98 7.93 25 CLS-3 34.34 33.42 4.29 0.64 24 CLS-4 30.99 31.46 3.87 10.33 25 CLS-5 31.77 30.70 3.97 8.07 26 CLS-6 32.82 32.75 4.10 5.03 24 均值 32.37 32.03 4.05 6.34 25
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