Study on the Re-Loaded Mechanical Properties of Pre-Peak Unloading Damage Mudstone

Zhao Jingfeng; Che Delong; Zhao Erping; Zhang Cong; Wei Yuhang

doi:10.20174/j.JUSE.2026.02.12

Chinese Journal of Underground Space and Engineering >

2026 , Vol. 22 >Issue 2: 506 - 516

DOI: https://doi.org/10.20174/j.JUSE.2026.02.12

Study on the Re-Loaded Mechanical Properties of Pre-Peak Unloading Damage Mudstone

Zhao Jingfeng ,
Che Delong ,
Zhao Erping ,
Zhang Cong ,
Wei Yuhang

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1. China Railway Eryuan Engineering Group Co., Ltd., Chengdu 610031, P.R. China;
2. Key Laboratory of Geological Hazards on Three Gorges Reservoir Area, Ministry of Education, Yichang, Hubei 443002, P.R. China;
3. College of Civil Engineering and Architecture, China Three Gorges University, Yichang, Hubei 443002, P.R. China

Received date: 2025-04-05

Online published: 2026-04-28

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Abstract

The reloading mechanical properties of the surrounding rock in an underground energy storage cavern are crucial for determining the safety of underground energy storage projects. This study conducted triaxial loading and unloading tests on mudstone, as well as reloading tests on unloaded damaged mudstone. By employing testing and analysis techniques such as nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM), the research investigated the impact of unloading effects on the reloading mechanical properties of mudstone and revealed the deterioration mechanisms of reloading damaged mudstone. The results indicate that the fractal dimension ultimately decreases as confining pressure increases, and the confining pressure's control over internal micro-cracks in the mudstone becomes more pronounced. With increasing unloading damage, small-size micro-pores inside the mudstone samples develop into medium-sized pores, resulting in a higher internal porosity. The greater the initial unloading damage, the larger the reduction in reloading strength of the mudstone. The degree of unloading damage progressively affects the failure mode of rock samples, transitioning from shear failure to shear-tensile failure, and eventually to tensile-shear failure with increasing unloading damage. A correlation between unloading damage degree, porosity, and reloading strength has been established, bridging the gap between microstructural damage and macro-strength deterioration in unloaded damaged mudstone. This finding provides a reference for delineating unloading damage zones and predicting reloading strength within unloading areas.

Key words： rock mechanics; excavation unloading; reloading; dissipated energy; fractal dimension

Cite this article

Zhao Jingfeng , Che Delong , Zhao Erping , Zhang Cong , Wei Yuhang . Study on the Re-Loaded Mechanical Properties of Pre-Peak Unloading Damage Mudstone[J]. Chinese Journal of Underground Space and Engineering, 2026 , 22(2) : 506 -516 . DOI: 10.20174/j.JUSE.2026.02.12

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