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<p>The long-term creep behavior of deep rock masses represents a critical challenge for the safety assessment of underground engineering projects such as nuclear waste disposal and deep mining. Accurate prediction is hindered by laboratory limitations: conventional tests cannot reproduce in-situ stress histories or repair sampling-induced damage. In this study, a novel experimental approach incorporating in-situ stress restoration was applied to triaxial unloading creep tests on red sandstone specimens obtained from a depth of 1100 m, with unrestored samples serving as controls. Results reveal a dual effect of in-situ stress restoration: (i) it repairs initial micro-damage and significantly retards energy dissipation, extending the macroscopic creep lifetime by more than 75%; (ii) however, analysis based on the Monkman–Grant relation indicates that steady-state creep strain decreases by approximately 32%. This paradox of “longer lifetime but reduced failure strain” reflects a transition in failure mode—from progressive ductile failure governed by diffuse microcrack accumulation in unrestored samples, to brittle failure dominated by rapid propagation of major cracks in restored samples. SEM fracture analysis revealed that fracture surfaces in the in-situ stress recovery group were dominated by dense ductile pits, featuring low crack density and opening, indicative of dispersed plastic energy dissipation. In contrast, the direct creep test group exhibited large, flat cleavage planes and through-cracking brittle fractures, with cracks propagating rapidly along weak surfaces. These findings reveal that stress recovery reduces fracture network connectivity through micro-damage densification, thereby delaying unstable crack propagation and shifting the macroscopic failure mode from progressive ductile failure to more localized, abrupt brittle instability. This insight holds significant implications for stability assessment in deep mining and tunnel engineering. The in-situ stress recovery process can serve as a potential technical measure to extend rock mass service life and optimize construction procedures.</p>

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Study on the dual effects of In-situ stress recovery on unloading creep behavior and failure mechanism of deep red sandstone

  • 期刊论文

  • 发表日期：

    2026年3月23日

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  • Shi Ji,
  • Sun Yi,
  • Zhang Jing,
  • Li Kegang

摘要

The long-term creep behavior of deep rock masses represents a critical challenge for the safety assessment of underground engineering projects such as nuclear waste disposal and deep mining. Accurate prediction is hindered by laboratory limitations: conventional tests cannot reproduce in-situ stress histories or repair sampling-induced damage. In this study, a novel experimental approach incorporating in-situ stress restoration was applied to triaxial unloading creep tests on red sandstone specimens obtained from a depth of 1100 m, with unrestored samples serving as controls. Results reveal a dual effect of in-situ stress restoration: (i) it repairs initial micro-damage and significantly retards energy dissipation, extending the macroscopic creep lifetime by more than 75%; (ii) however, analysis based on the Monkman–Grant relation indicates that steady-state creep strain decreases by approximately 32%. This paradox of “longer lifetime but reduced failure strain” reflects a transition in failure mode—from progressive ductile failure governed by diffuse microcrack accumulation in unrestored samples, to brittle failure dominated by rapid propagation of major cracks in restored samples. SEM fracture analysis revealed that fracture surfaces in the in-situ stress recovery group were dominated by dense ductile pits, featuring low crack density and opening, indicative of dispersed plastic energy dissipation. In contrast, the direct creep test group exhibited large, flat cleavage planes and through-cracking brittle fractures, with cracks propagating rapidly along weak surfaces. These findings reveal that stress recovery reduces fracture network connectivity through micro-damage densification, thereby delaying unstable crack propagation and shifting the macroscopic failure mode from progressive ductile failure to more localized, abrupt brittle instability. This insight holds significant implications for stability assessment in deep mining and tunnel engineering. The in-situ stress recovery process can serve as a potential technical measure to extend rock mass service life and optimize construction procedures.