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<p>Understanding the frictional dynamics in tectonic faults under the condition of variable normal stress is critical for elucidating earthquake mechanisms. This study investigates the stick–slip behavior of saw-cut granite joints under cyclic normal stress via laboratory double-direct shear tests and physical models. Experiments are conducted under various amplitudes (10–80% of mean value) and frequencies (0.1–0.8&#xa0;Hz) of cyclic normal stress, with a constant mean stress of 3&#xa0;MPa. An improved Spring-Block (SB) model incorporating Rate and State (RS) friction law is utilized to analyze slip behavior and transient contact area evolution. Results reveal systematic transitions in slip styles: chaotic slip at low amplitudes and compound slip (alternating large and small slip events) at high amplitudes. Frequency variation of cyclic normal stress induces resonance effects, with a critical frequency triggering the lowest shear strength. Simulations by the physical model underscore the advantage of RS friction laws compared to Coulomb friction. The speculated joint contact density based on theoretical equations is affected by both, normal stress cycles and state variable (<i>θ</i>) variation. The rapid slip effect greatly reduces the speculated contact area and the curvature radius of contacted asperity. These findings highlight that joint/fault instability is governed by coupled interactions between normal stress perturbations, contact area variations, and frictional state transitions.</p>

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Stick–Slip Friction and Surface Contact Density of Bare Granite Joint Affected by Cyclic Normal Stress

  • 期刊论文

  • 发表日期：

    2025年11月18日

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  • Kang Tao,
  • Heinz Konietzky,
  • Fuqiang Gao,
  • Rui Wu,
  • Wengang Dang,
  • Chenghao Li,
  • Yu Liu

摘要

Understanding the frictional dynamics in tectonic faults under the condition of variable normal stress is critical for elucidating earthquake mechanisms. This study investigates the stick–slip behavior of saw-cut granite joints under cyclic normal stress via laboratory double-direct shear tests and physical models. Experiments are conducted under various amplitudes (10–80% of mean value) and frequencies (0.1–0.8 Hz) of cyclic normal stress, with a constant mean stress of 3 MPa. An improved Spring-Block (SB) model incorporating Rate and State (RS) friction law is utilized to analyze slip behavior and transient contact area evolution. Results reveal systematic transitions in slip styles: chaotic slip at low amplitudes and compound slip (alternating large and small slip events) at high amplitudes. Frequency variation of cyclic normal stress induces resonance effects, with a critical frequency triggering the lowest shear strength. Simulations by the physical model underscore the advantage of RS friction laws compared to Coulomb friction. The speculated joint contact density based on theoretical equations is affected by both, normal stress cycles and state variable (θ) variation. The rapid slip effect greatly reduces the speculated contact area and the curvature radius of contacted asperity. These findings highlight that joint/fault instability is governed by coupled interactions between normal stress perturbations, contact area variations, and frictional state transitions.