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Combined effect of pore water pressure and axial stress level on the unloading mechanical properties of sandstone

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Abstract

For the stability evaluation of excavation engineering located in reservoirs, the combined effect of pore water pressure P and axial stress level ASL on the unloading mechanical properties of rocks is significant to study. The loading and unloading tests were performed on the sandstone under different Ps and ASLs, and a novel method was proposed for evaluating the damage degree caused by the P and the unloading of confining stress during the unloading process of samples. The results showed that the strength and the unloaded amount of the sandstone decrease with the applied ASL and P. The area of cracks generated during the unloading increases with the P and ASL, indicating a higher damage degree under higher P and ASL. The development orientation of the crack is more inclined to the unloading direction under lower ASL and P, due to a larger unloading amount. The damage degree caused by the unloading of confining stress is higher under lower ASL, while the effect of P on the damage degree of samples is greater under higher ASL. It demonstrates that the developed method can be used for evaluating the damage degree of rocks during the unloading process, especially caused by the pore water pressure, while the traditional method cannot.

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Abbreviations

ASL :

Axial stress level

P :

Pore water pressure

σ 3 :

Confining stress

σ 1 :

Axial stress

ε 1 :

Axial strain

F :

Increment of deviatoric stress

d :

Unloading amount of confining stress

\(\Delta \varepsilon {\prime}\) :

Axial strain confining stress compliance

D i :

Traditional unloading damage parameter

D :

Developed unloading damage coefficient

D u :

Damage degree caused by the unloading of confining stress

D p :

Damage degree caused by the pore water pressure

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Funding

This study is funded by the High Speed Rail Joint Fund (No. U2034203), National Natural Science Foundation of China (No. 42207218), National Natural Science Foundation of China (No. U23A2045), Natural Science Foundation of Hubei Province (No. 2020CFA049), Guangdong Basic and Applied Basic Research Foundation (2021A1515110723).

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Authors and Affiliations

  1. Key Laboratory of Geological Hazards on Three Gorges Reservoir Area (China Three Gorges University), Ministry of Education, Yichang, 443002, China

    Erping Zhao, Han Zhang, Guoliang Xiang & Lehua Wang

  2. College of Civil Engineering & Architecture, China Three Gorges University, Yichang, 443002, China

    Erping Zhao, Han Zhang, Guoliang Xiang & Lehua Wang

Authors
  1. Erping Zhao
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  2. Han Zhang
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  3. Guoliang Xiang
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  4. Lehua Wang
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Corresponding author

Correspondence to Han Zhang.

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Zhao, E., Zhang, H., Xiang, G. et al. Combined effect of pore water pressure and axial stress level on the unloading mechanical properties of sandstone. Bull Eng Geol Environ 83, 150 (2024). https://doi.org/10.1007/s10064-024-03651-8

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  • DOI: https://doi.org/10.1007/s10064-024-03651-8

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