<p>The stability of underground surrounding rock is critically influenced by the progressive shear failure and brittle instability characteristics of rock joints. To investigate the shear instability mechanism underlying deep underground disasters, shear tests were conducted on rough symmetrical joints under constant normal stiffness conditions. The study examined the effects of initial normal stress (2–6 MPa), normal stiffness (2.5–10.0 GPa/m), and joint roughness coefficient (JRC) on shear instability progression and failure morphology. Results indicate that peak shear strength increases significantly with higher initial normal stress, normal stiffness, or JRC. Progressive failure evolves through three distinct stages: near-linear climbing, climbing abrasion, and cutting failure. Increased normal stiffness constrains the effects of undulation dilation and climbing, leading to a shift in the cutting failure initiation site from the undulation apex to the root region. Based on the shear stress–shear displacement curves, the energy characteristics of joints were analyzed, encompassing the pre-peak elastic energy, pre-peak plastic energy, post-peak dissipated energy, and post-peak residual elastic energy during the shearing process. This analysis clarified the energy mechanism underlying the post-peak failure modes of joint shearing under different stiffness conditions. A dimensionless ratio (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">$\beta$</EquationSource> <EquationSource Format="MATHML"><math> <mi>β</mi> </math></EquationSource> </InlineEquation>) related to pre-peak elastic energy storage and post-peak energy dissipation was proposed to quantify shear brittleness of joints. Unstable failure (<InlineEquation ID="IEq2"> <EquationSource Format="TEX">$\beta > 1$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>β</mi> <mo>></mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation>) occurs when pre-peak stored energy is sufficient to drive post-peak deformation, whereas stable failure (<InlineEquation ID="IEq3"> <EquationSource Format="TEX">$\beta < 1$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>β</mi> <mo><</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation>) ensues from an energy deficit. Comparative analysis with established indices reveal that joints with higher normal stiffness and roughness exhibit greater brittle disaster propensity. The proposed brittleness index offers novel insights into the disaster-inducing propensity of joints and facilitates the assessment engineering surrounding rock stability.</p>

Experimental Study on the Shear Behavior and Instability of Rough Symmetrical Joints Under Constant Normal Stiffness Conditions

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发表日期：

2025年10月16日

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Jianan Yang,
Pengxian Fan,
Sheng Li,
Jie Li,
Haozhe Xing,
Chao Li

摘要

The stability of underground surrounding rock is critically influenced by the progressive shear failure and brittle instability characteristics of rock joints. To investigate the shear instability mechanism underlying deep underground disasters, shear tests were conducted on rough symmetrical joints under constant normal stiffness conditions. The study examined the effects of initial normal stress (2–6 MPa), normal stiffness (2.5–10.0 GPa/m), and joint roughness coefficient (JRC) on shear instability progression and failure morphology. Results indicate that peak shear strength increases significantly with higher initial normal stress, normal stiffness, or JRC. Progressive failure evolves through three distinct stages: near-linear climbing, climbing abrasion, and cutting failure. Increased normal stiffness constrains the effects of undulation dilation and climbing, leading to a shift in the cutting failure initiation site from the undulation apex to the root region. Based on the shear stress–shear displacement curves, the energy characteristics of joints were analyzed, encompassing the pre-peak elastic energy, pre-peak plastic energy, post-peak dissipated energy, and post-peak residual elastic energy during the shearing process. This analysis clarified the energy mechanism underlying the post-peak failure modes of joint shearing under different stiffness conditions. A dimensionless ratio ( $\beta$ $β$ ) related to pre-peak elastic energy storage and post-peak energy dissipation was proposed to quantify shear brittleness of joints. Unstable failure ( $\beta > 1$ $β > 1$ ) occurs when pre-peak stored energy is sufficient to drive post-peak deformation, whereas stable failure ( $\beta < 1$ $β < 1$ ) ensues from an energy deficit. Comparative analysis with established indices reveal that joints with higher normal stiffness and roughness exhibit greater brittle disaster propensity. The proposed brittleness index offers novel insights into the disaster-inducing propensity of joints and facilitates the assessment engineering surrounding rock stability.