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<p>Granitic residual soil (GRS) is widely distributed across the hilly regions of southeastern China, and understanding its microstructural evolution under increasing moisture is critical for elucidating the mechanisms of soil erosion and landslides. This study establishes a multiscale analytical framework that integrates nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and direct shear tests on GRS samples across a moisture spectrum from 10% to saturation. The results reveal a three‑stage pore evolution with increasing moisture content. In the pore activation stage (ω = 10–20%), bound water dominates, promoting face‑to‑face particle contact and strain softening behavior. As moisture increases to the pore coalescence stage (ω = 20–30%), capillary water surpasses bound water, triggering microcrack expansion, edge‑to‑face contact, and a transition to strain hardening. Upon saturation (the pore collapse stage), a surge in free water disintegrates macropores into mesopores, causing a sharp cohesion loss of 36.2%. A critical moisture threshold of 25–30% is identified by the convergence of the NMR water‑type transition, mechanical inflection in cohesion, and SEM‑derived porosity change. Mechanical degradation follows a “moisture‑pore‑mechanics” cascade. For field application, the laboratory thresholds are translated into volumetric water content, with θ = 0.33 serving as an early warning for pore coalescence and θ = 0.39 indicating imminent collapse, which can be monitored in real time using low‑cost soil moisture sensors. Collectively, these findings provide a microstructural basis for understanding hydrologically induced failure mechanisms in GRS slopes and establish theoretical foundations for critical moisture warning systems and intelligent drainage design.</p>

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Wetting-induced microstructural evolution and mechanical degradation of granitic residual soils in Southeastern China

  • 期刊论文

  • 发表日期：

    2026年7月3日

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  • Xiaoyu Yi,
  • Wenkai Feng,
  • Huilin Bai,
  • Shuangquan Li,
  • Jiachen Zhao,
  • Yanlong Zhao

摘要

Granitic residual soil (GRS) is widely distributed across the hilly regions of southeastern China, and understanding its microstructural evolution under increasing moisture is critical for elucidating the mechanisms of soil erosion and landslides. This study establishes a multiscale analytical framework that integrates nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and direct shear tests on GRS samples across a moisture spectrum from 10% to saturation. The results reveal a three‑stage pore evolution with increasing moisture content. In the pore activation stage (ω = 10–20%), bound water dominates, promoting face‑to‑face particle contact and strain softening behavior. As moisture increases to the pore coalescence stage (ω = 20–30%), capillary water surpasses bound water, triggering microcrack expansion, edge‑to‑face contact, and a transition to strain hardening. Upon saturation (the pore collapse stage), a surge in free water disintegrates macropores into mesopores, causing a sharp cohesion loss of 36.2%. A critical moisture threshold of 25–30% is identified by the convergence of the NMR water‑type transition, mechanical inflection in cohesion, and SEM‑derived porosity change. Mechanical degradation follows a “moisture‑pore‑mechanics” cascade. For field application, the laboratory thresholds are translated into volumetric water content, with θ = 0.33 serving as an early warning for pore coalescence and θ = 0.39 indicating imminent collapse, which can be monitored in real time using low‑cost soil moisture sensors. Collectively, these findings provide a microstructural basis for understanding hydrologically induced failure mechanisms in GRS slopes and establish theoretical foundations for critical moisture warning systems and intelligent drainage design.