Abstract
The progressive brittle failure of high-stress hard surrounding rock masses caused by layered excavation severely threatens the stability of large underground caverns. We summarize the stress path in the potential failure zone of the Shuangjiangkou underground powerhouse during layered excavation, and then design the multistep unloading confining pressure test and the cyclic loading–unloading test with multistep unloading confining pressure. The deformation, strength, acoustic emission, and failure characteristics of granite, as well as the evolution of critical stress thresholds and mechanical parameters are analyzed based on experimental results under different stress paths. The peak strength of the rock significantly depends on the stress path and the amount of unloading confining pressure. The rock failure process under multistep unloading confining pressure is divided into stable and unstable crack growth stages, with the failure mode shifting from tensile cracks to mixed tensile–shear cracks. The evolution modes of critical stress thresholds, cohesion, and internal friction angle with amount of unloading confining pressure differ significantly from that with the equal plastic strain. The former is nearly linear, while the latter is exponentially nonlinear. The evolution of the deformation modulus, cohesion, and internal friction angle confirms the rationality of the cohesion-weakening–friction-strengthening model with degraded deformation modulus for the stability analysis of surrounding rock masses under layered excavation. The experimental methods for obtaining the evolution of rock mechanical parameters using a single specimen under unloading confining pressure are also discussed. The results imply that the layered excavation-induced nonlinear deterioration of the deformation modulus and strength parameters of high-stress hard surrounding rock masses should be considered in the stability analysis of large underground caverns. Further, the timely compensation of the excavation-induced confining pressure loss is critical to ensure the stability of high-stress hard surrounding rock masses under layered excavation.
Highlights
-
A stress path was designed to reflect the stress evolution characteristics for rock masses of the large underground cavern under layered excavation;
-
The deformation, strength, acoustic emission, and failure characteristics of granite under the layered excavation stress path were analyzed;
-
The evolution of rock mechanical parameters with unloading confining pressure and the equivalent plastic strain were obtained;
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An experimental method for obtaining the evolution of rock mechanical parameters using a single specimen under unloading confining pressure was discussed.
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Data will be made available on request.
Abbreviations
- MSUCPT:
-
Multistep unloading confining pressure test
- CLUT-MSUCP:
-
Cyclic loading–unloading with multistep unloading confining pressures
- IASDCPT:
-
Increasing axial stress and decreasing confining pressure test
- MASDCPT:
-
Maintaining axial stress and decreasing confining pressure test
- CLUT-CCP:
-
Cyclic loading–unloading test with the constant confining pressure
- CLUT-MSLCP:
-
Cyclic loading–unloading test with multistep loading confining pressure
- CTCT:
-
Conventional triaxial compression test
- AE:
-
Acoustic emission
- \(\sigma_{1}^{{}}\) :
-
Maximum principal stress
- \(\sigma_{1}^{0}\) :
-
Initial axial stress of unloading test
- \(\sigma_{3}^{0}\) :
-
Initial confining pressure
- \(\Delta \sigma_{3}^{{}}\) :
-
Amount of unloading confining pressure
- CI :
-
Crack initiation stress threshold
- \(k_{{{\text{cd}}}}^{{}}\) :
-
Slope of fitting line for CD vs \(\sigma_{3}^{0}\)
- \(\varepsilon_{1}^{{}}\) :
-
Axial strain
- \(\varepsilon_{{\text{v}}}^{{}}\) :
-
Volumetric strain
- \(\varepsilon_{{}}^{{\text{p}}}\) :
-
Plastic strain
- \(\varepsilon_{3}^{{\text{e}}}\) :
-
Elastic lateral strain
- \(\varepsilon_{1}^{{\text{p}}}\) :
-
Plastic axial strain
- \(\varepsilon_{{\text{v}}}^{{\text{p}}}\) :
-
Plastic volumetric strain
- \(E_{{\text{u}}}\) :
-
Unloading modulus
- \(c_{{}}^{{}}\) :
-
Cohesion
- \(\sigma_{3}^{{}}\) :
-
Minimum principal stress
- \(\sigma_{1}^{{\text{f}}}\) :
-
Axial stress at failure
- \(\sigma_{3}^{{\text{f}}}\) :
-
Confining pressure at failure
- \(\Delta \sigma_{3}^{0}\) :
-
Amount of single-step unloading confining pressure
- CD :
-
Crack damage stress threshold
- \(\varepsilon_{1}^{{\text{f}}}\) :
-
Axial strain at failure
- \(\varepsilon_{3}^{{}}\) :
-
Lateral strain
- \(\varepsilon_{{}}^{{\text{e}}}\) :
-
Elastic strain
- \(\varepsilon_{1}^{{\text{e}}}\) :
-
Elastic axial strain
- \(\varepsilon_{{\text{v}}}^{{\text{e}}}\) :
-
Elastic volumetric strain
- \(\varepsilon_{3}^{{\text{p}}}\) :
-
Plastic lateral strain
- \(\varepsilon_{{\text{p}}}^{{}}\) :
-
Equivalent plastic strain
- \(\mu_{{\text{u}}}\) :
-
Apparent Poisson’s ratio
- \(\varphi\) :
-
Internal friction angle
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Acknowledgements
This research was funded by the National Natural Science Foundation of China (Grant No. 51979268). In particular, the authors also wish to thank Prof. Hua Zhang from State Key Laboratory of Geomechanics and Geotechnical Engineering, who gave support and assistance during the triaxial unloading tests.
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Xia, Y., Xu, D., Qiu, S. et al. Experimental Study on Mechanical Properties of Deeply Buried Granite During Layered Excavation of Large Underground Caverns. Rock Mech Rock Eng 56, 4757–4778 (2023). https://doi.org/10.1007/s00603-023-03304-4
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DOI: https://doi.org/10.1007/s00603-023-03304-4