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<p>This study presents a detailed investigation into stress-induced failure mechanisms in a shallow, large-span cavern excavated in horizontally bedded Hawkesbury Sandstone under elevated horizontal in situ stress. The cavern roof comprises a laminated rock beam bounded by a clay-infilled bedding plane and intersected by low-angled, non-persistent cross-bedding, features that became structurally adverse under high stress. Field observations, including endoscopic imaging, geological mapping, displacement monitoring, and shotcrete lining crack patterns, enabled direct tracking of roof beam crack propagation and its correlation with bedding shear and in-cavern deformation. A three-dimensional numerical back analysis using 3DEC was conducted to calibrate in situ stress conditions and simulate excavation-induced deformation. The analysis revealed horizontal stress magnitudes approximately 30% higher than empirical predictions and successfully replicated observed failure mechanisms, including tensile-shear cracking, bedding shear exceeding 30&#xa0;mm, and shotcrete delamination. The study identifies a tensile–shear interaction as the governing failure mechanism, validates the application of the cohesion weakening and friction strengthening (CWFS) model for laminated Hawkesbury Sandstone, and proposes a bedding shear threshold for re-bolting. The effectiveness of surface settlement control measures, such as staged excavation and second-pass longer cable-type bolts, was validated through both simulation and field monitoring. To the author’s knowledge, this is the first documented case in Sydney where stress-induced failure mechanisms were directly observed in a shallow cavern, offering rare insights into laminated rock beam behaviour under elevated horizontal stress conditions. While unique to Sydney, these insights address challenges common to shallow, large-span caverns internationally, where high horizontal stress affects laminated rock beams. Despite adverse geological and stress conditions, the primary support system maintained global and local stability. The findings contribute to safer and more resilient underground design strategies in sedimentary formations worldwide.</p>

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Stress-Induced Failure Mechanisms of a Shallow, Large-Span Cavern: Insights from Field Observations and Numerical Back analysis

  • 期刊论文

  • 发表日期：

    2026年1月28日

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  • Sivanathan Thirukumaran

摘要

This study presents a detailed investigation into stress-induced failure mechanisms in a shallow, large-span cavern excavated in horizontally bedded Hawkesbury Sandstone under elevated horizontal in situ stress. The cavern roof comprises a laminated rock beam bounded by a clay-infilled bedding plane and intersected by low-angled, non-persistent cross-bedding, features that became structurally adverse under high stress. Field observations, including endoscopic imaging, geological mapping, displacement monitoring, and shotcrete lining crack patterns, enabled direct tracking of roof beam crack propagation and its correlation with bedding shear and in-cavern deformation. A three-dimensional numerical back analysis using 3DEC was conducted to calibrate in situ stress conditions and simulate excavation-induced deformation. The analysis revealed horizontal stress magnitudes approximately 30% higher than empirical predictions and successfully replicated observed failure mechanisms, including tensile-shear cracking, bedding shear exceeding 30 mm, and shotcrete delamination. The study identifies a tensile–shear interaction as the governing failure mechanism, validates the application of the cohesion weakening and friction strengthening (CWFS) model for laminated Hawkesbury Sandstone, and proposes a bedding shear threshold for re-bolting. The effectiveness of surface settlement control measures, such as staged excavation and second-pass longer cable-type bolts, was validated through both simulation and field monitoring. To the author’s knowledge, this is the first documented case in Sydney where stress-induced failure mechanisms were directly observed in a shallow cavern, offering rare insights into laminated rock beam behaviour under elevated horizontal stress conditions. While unique to Sydney, these insights address challenges common to shallow, large-span caverns internationally, where high horizontal stress affects laminated rock beams. Despite adverse geological and stress conditions, the primary support system maintained global and local stability. The findings contribute to safer and more resilient underground design strategies in sedimentary formations worldwide.