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<p>Rock discontinuities exert a primary control on the stability of rock masses, and their shear strength is strongly influenced by moisture conditions and weathering. However, the coupled effects of water saturation and intrinsic rock characteristics, including mineralogy, surface hardness, and weathering grade, on the basic friction angle (φᵦ) remain incompletely quantified. This study investigates granite, marble, and limestone from Khyber Pakhtunkhwa, Pakistan, providing a comparative dataset relevant to regional engineering practice. Fifteen rock samples spanning weathering grades WG I to WG III (five per lithology) were tested using multi-stage direct shear (DST) and tilt shear (TST) methods on planar, saw-cut discontinuities under dry, saturated-surface-dry (SSD), and fully saturated conditions. Basic friction angles were evaluated alongside ultrasonic pulse velocity (UPV), Schmidt rebound hardness (SRH), and petrographic mineralogy. Results show that moisture consistently reduces joint shear strength, with φᵦ decreasing by approximately 10–20% upon saturation across all lithologies (for example, limestone from 30.9° in dry conditions to 26.9° when saturated). Under dry conditions, limestone exhibited the highest φᵦ values (approximately 30°), marble intermediate values (approximately 26–28°), and granite the lowest (approximately 22–25°). Within the tested dataset, fresh, dense limestone samples retained higher frictional resistance under wet conditions than more weathered granite and marble samples. The basic friction angle correlates positively with SRH and UPV, reflecting the influence of surface condition and weathering-related microstructural degradation, whereas bulk modal mineral proportions alone do not show a direct linear relationship with φᵦ. These findings indicate that mineralogy influences joint strength primarily through its control on weathering susceptibility and surface degradation mechanisms rather than through mineral percentages alone. The results demonstrate that groundwater exposure can substantially weaken rock joints, highlighting the importance of incorporating moisture-adjusted friction angles into slope, tunnel, and foundation design. The integrated mechanical and non-destructive testing framework presented here provides a practical basis for assessing joint strength degradation in humid and groundwater-affected rock engineering environments.</p>

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Integrated Mechanical–NDT Evaluation of Moisture- and Weathering-Induced Weakening in Granite, Marble, and Limestone Joints

  • 期刊论文

  • 发表日期：

    2026年3月13日

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  • Waqas Ahmed,
  • Azhar Ali,
  • Abdul Rahim Asif,
  • M. E. Al-Atroush,
  • Muhammad Yasir

摘要

Rock discontinuities exert a primary control on the stability of rock masses, and their shear strength is strongly influenced by moisture conditions and weathering. However, the coupled effects of water saturation and intrinsic rock characteristics, including mineralogy, surface hardness, and weathering grade, on the basic friction angle (φᵦ) remain incompletely quantified. This study investigates granite, marble, and limestone from Khyber Pakhtunkhwa, Pakistan, providing a comparative dataset relevant to regional engineering practice. Fifteen rock samples spanning weathering grades WG I to WG III (five per lithology) were tested using multi-stage direct shear (DST) and tilt shear (TST) methods on planar, saw-cut discontinuities under dry, saturated-surface-dry (SSD), and fully saturated conditions. Basic friction angles were evaluated alongside ultrasonic pulse velocity (UPV), Schmidt rebound hardness (SRH), and petrographic mineralogy. Results show that moisture consistently reduces joint shear strength, with φᵦ decreasing by approximately 10–20% upon saturation across all lithologies (for example, limestone from 30.9° in dry conditions to 26.9° when saturated). Under dry conditions, limestone exhibited the highest φᵦ values (approximately 30°), marble intermediate values (approximately 26–28°), and granite the lowest (approximately 22–25°). Within the tested dataset, fresh, dense limestone samples retained higher frictional resistance under wet conditions than more weathered granite and marble samples. The basic friction angle correlates positively with SRH and UPV, reflecting the influence of surface condition and weathering-related microstructural degradation, whereas bulk modal mineral proportions alone do not show a direct linear relationship with φᵦ. These findings indicate that mineralogy influences joint strength primarily through its control on weathering susceptibility and surface degradation mechanisms rather than through mineral percentages alone. The results demonstrate that groundwater exposure can substantially weaken rock joints, highlighting the importance of incorporating moisture-adjusted friction angles into slope, tunnel, and foundation design. The integrated mechanical and non-destructive testing framework presented here provides a practical basis for assessing joint strength degradation in humid and groundwater-affected rock engineering environments.