Key Takeaways & Executive Findings
- •• Long-term creep tests on Beishan granite under uniaxial compression reveal that specimens fail under sustained loads above a threshold, with durations ranging from 839 to 1204 days, while a specimen at 60 MPa survived over 1650 days. • A lower envelope of driving stress-ratio for crystalline rocks approaches approximately 0.45 over infinite time, providing a critical reference for long-term strength assessment. • Both transient creep strain and steady-state creep rate increase exponentially with axial stress, while the steady-state creep strain contribution remains constant at about 82.53%. • A novel damage-based creep model accurately predicts the accelerated creep phase, enhancing the reliability of long-term stability evaluations for engineering structures such as deep geological repositories.
Abstract
Investigations into the long-term creep behavior of Beishan granite in uniaxial compression were conducted. Four levels of axial stress (60, 70, 87, and 95 MPa) were applied to rock specimens. Contrasting with earlier research, the long-term creep data in this work present a substantial advancement in the time dimension. Except for the sample subjected to 60 MPa axial loading, which did not fail after a loading duration of 1650 d, the specimens under the other three stresses all failed after sustained constant loading durations of 1204, 1023, and 839 d, respectively. A lower envelope of driving stress-ratio for crystalline rocks was obtained, tending towards approximately 0.45 over an infinite time scale. According to the experimental results, as axial stress increases, both the axial strain accumulated in the transient creep process and the strain rate associated with steady-state creep deformation increase exponentially; however, the share of steady-state creep strain remains nearly constant at about 82.53 %. A novel damage-based creep model was put forward. It provides an enhanced depiction of the comprehensive creep process in rocks, notably improving the accuracy in forecasting the accelerated creep phase, which significantly impacts the long-term stability of engineering structures.
1. Introduction
High-level radioactive waste (HLW) is the inevitable product of the development of the nuclear industry. The HLW necessitates isolation from the biosphere over exceptionally long durations, owing to its prolonged half-life and elevated radioactivity levels. Deep geological repository is globally recognized as a viable strategy for the permanent containment of HLW. Crystalline rock such as granite, which is characterized by high strength, low permeability, and good thermal conductivity, has been considered one of favourable rock types for hosting deep geological repositories (DGRs). Meanwhile, many underground research laboratories (URLs) for geological disposal have been or are being built in crystalline rock formations for the development of DGRs [1].
The safety strategy of the DGRs of radioactive waste indicates that the isolation period of HLW from the human biosphere should be no less than ten thousand years. During the operation of a DGR, the rocks adjacent to the excavation perimeter endure prolonged pressure induced by the excavation process. Accurately assessing the long-term behavior of DGRs necessitates a comprehensive understanding of the temporal variations in the mechanical characteristics of the surrounding rock. If the long-term creep deformation of the surrounding rock around the deposition hole is excessive, it may cause the disposal container to be damaged, leading to the release of radionuclides and their migration to the biosphere through seepage pathways. The long-term creep behavior of the surrounding rock, which is the last line of defense separating radioactive nuclides from the biosphere, plays a crucial controlling role in the long-term stability and safety of the repository. Undoubtedly, a comprehensive comprehension of long-term creep characteristics of rocks is a prerequisite for assessing the long-term behavior of DGRs.
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Chunping Wang, Xingguang Zhao, Jianfeng Liu, Haiyang Zhang, Liang Chen, Hongsu Ma, Ju Wang (2025). Long-term creep of Beishan granite under uniaxial compression. International Journal of Mining Science and Technology. https://doi.org/10.1016/j.ijmst.2025.10.009
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Frequently Asked Questions
What is the long-term strength of Beishan granite?
The study suggests that the lower envelope of driving stress-ratio for crystalline rocks approaches approximately 0.45 over an infinite time scale, indicating that the long-term strength of Beishan granite is about 45% of its uniaxial compressive strength.
How long did the creep tests last?
The creep tests lasted up to 1650 days for the specimen at 60 MPa, which did not fail, while specimens at 70, 87, and 95 MPa failed after 1204, 1023, and 839 days, respectively.
What is the significance of the damage-based creep model?
The novel damage-based creep model provides an enhanced depiction of the comprehensive creep process in rocks, notably improving the accuracy in forecasting the accelerated creep phase, which is critical for assessing the long-term stability of engineering structures.
How does axial stress affect creep behavior?
As axial stress increases, both the axial strain accumulated in the transient creep process and the strain rate associated with steady-state creep deformation increase exponentially, while the share of steady-state creep strain remains nearly constant at about 82.53%.
Why is the study of long-term creep important for radioactive waste disposal?
Long-term creep of surrounding rock can cause deformation that may damage disposal containers, leading to the release of radionuclides. Understanding creep behavior is essential for ensuring the long-term stability and safety of deep geological repositories.
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