Unloading Behaviors of Shale under the Effects of Water Through Experimental and Numerical Approaches
Publication: International Journal of Geomechanics
Volume 22, Issue 6
Abstract
During tunnel excavations through shale formations in central and southwest China, engineering problems, such as large deformations and distorted arches, were encountered due to radial stress unloading and groundwater pressure. Few studies have been carried out on the issues exhibited by soft shale tunnels that have considered the comprehensive influence of unloading and water effects. To characterize the unloading behaviors, a series of conventional triaxial compression (CTC) tests and unloading confining pressure (UCP) tests were performed under drained conditions and compared. Based on theoretical and experimental analyses, deformation parameters from the UCP process were derived and compared with those from the CTC test. The stress–strain response, evolution of deformation and strength parameters, and postpeak mechanical behavior and failure modes were analyzed in order to reveal the unloading and water effects. To quantify the difference between the CTC and UCP behaviors in geotechnical practice, a tunnel excavation was simulated using the CTC and UCP models. The distributions of damage and displacement were analyzed in a numerical case study. The results showed the comprehensive dependency of shale behaviors on unloading and water effects. The numerical case revealed significant tunnel deformation and fewer plastic zones in the excavation when using the UCP model rather than the CTC model. To accurately simulate the deformation and damage distribution, this study provided a methodology for construction design using the UCP test and the model for unloading and water-affected geotechnical engineering.
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Acknowledgments
This study was supported by the National Natural Science Foundation of China (Grant No. 51704097), the Science Foundation of Henan Polytechnic University for Distinguished Young Scientists (Grant No. J2021-2), and the Key Research and Development Program of Henan Province, China (Grant Nos. 202102310244, 202102310289, and 212102310293).
Notation
The following symbols are used in this paper:
- c
- cohesion;
- E
- elastic modulus in the loading process;
- Eu
- apparent unloading modulus;
- E′
- elastic modulus in the unloading process;
- J2
- second deviatoric stress invariant;
- function of dilation angle;
- p
- hydrostatic pressure;
- q
- equivalent shear stress;
- ɛ1, ɛ3
- major and minor principal strains;
- ɛ1r, ɛ3r
- residual maximum and minimum principal strains;
- , ,
- maximum, intermediate, and minimum principal plastic strains;
- ,
- residual maximum and minimum principal plastic strains;
- plastic volumetric strain;
- κs
- hardening parameter;
- σ1, σ2, σ3
- major, intermediate, and minor principal stresses;
- σ1r, σ3r
- residual maximum and minimum principal stresses;
- υ
- Poisson’s ratio in the loading process;
- υu
- apparent unloading Poisson’s ratio;
- υ′
- Poisson’s ratio in the unloading process;
- φ
- internal friction angle; and
- ψ
- dilation angle.
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Published In
International Journal of Geomechanics
Volume 22 • Issue 6 • June 2022
Copyright
© 2022 American Society of Civil Engineers.
History
Received: Mar 19, 2021
Accepted: Dec 9, 2021
Published online: Apr 6, 2022
Published in print: Jun 1, 2022
Discussion open until: Sep 6, 2022
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