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ZHANG Zhenyuan，LI Jinqiu，ZHANG Yongshuang，et al. Strength degradation characteristics of slip zone soil under different water contents and their effects on stability of Yahuokou landslide in Zhouqu County, Gansu Province[J]. Bulletin of Geological Science and Technology，2026，45（5）：1-14 doi: 10.19509/j.cnki.dzkq.tb20250207
Citation: ZHANG Zhenyuan，LI Jinqiu，ZHANG Yongshuang，et al. Strength degradation characteristics of slip zone soil under different water contents and their effects on stability of Yahuokou landslide in Zhouqu County, Gansu Province[J]. Bulletin of Geological Science and Technology，2026，45（5）：1-14 doi: 10.19509/j.cnki.dzkq.tb20250207
shu

Strength degradation characteristics of slip zone soil under different water contents and their effects on stability of Yahuokou landslide in Zhouqu County, Gansu Province

doi: 10.19509/j.cnki.dzkq.tb20250207

  • School of Engineering and Technology, China University of Geosciences (Beijing), Beijing 100083, China

  • Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences, Shijiazhuang 050061, China

  • First Institute of Geological and Mineral Exploration, Gansu Provincial Bureau of Geology and Mineral Resources, Tianshui Gansu 741020, China

  • Gansu Provincial Engineering Research Center for Comprehensive Exploration, Utilization and Protection of Mineral Resources, Tianshui Gansu 741020, China

More Information
    Abstract
  • Objective 

    The Yahuokou landslide in Zhouqu County, Gansu Province, is a typical large creeping landslide distributed along the Bailong River Fault Zone. Heavy rainfall in 2019 triggered large-scale sliding, causing major economic losses. Similar carbonaceous slate landslides are widely developed in this area. However, previous studies have mainly focused on macroscopic surface deformation monitoring of local landslides, lacking quantitative ring shear tests on strength degradation of slip zone soil under different water contents. In addition, the control mechanism of through-going tensile fractures on rainfall infiltration and slip zone softening remains unclear, and the zoned evolution of landslide instability has not been verified numerically. This restricts the formulation of refined landslide prevention and control schemes. This study aims to clarify the instability mechanism of Yahuokou landslide.

    Methods 

    Integrated UAV photogrammetry and field zoned detailed geological surveys were carried out. Argillized carbonaceous slate slip zone soil sampled from the rear edge of the landslide was subjected to multiple long-distance ring shear tests, with four water contents (9%, 12%, 15%, and 18% saturated) and three normal stress levels (100, 200, and 400 kPa). After shearing, three-dimensional laser scanning and scanning electron microscopy (SEM) were used to quantitatively calculate the root-mean-square relative roughness Z2 and observe the micro-morphology of shear surfaces. Based on FLAC3D, two numerical models with and without fractures were established. Three rainfall scenarios (light, moderate, heavy) were set, and 17 monitoring points were arranged to track the time-series evolution of saturation, pore water pressure, and slope displacement.

    Results 

    Field investigation showed that the landslide was in a long-term creep state, with severe deformation occurring in the rear source zone. The exposed carbonaceous slate slip zone soil had a clay particle content of 26.4% and a hydrophilic clay mineral content of approximately 52%, indicating high water sensitivity. Under long-distance shearing, the soil exhibited significant strain-softening characteristics, with a maximum softening ratio of 57.2%. When water content increased from 9% to saturated state, the overall shear strength decreased by 45.49%, and the maximum decrease in shear surface roughness Z2 was 0.24. Clay minerals formed face-to-face aggregative orientation layers on shear surfaces, developing a lubricating structure. The Z2 value was strongly positively correlated with the residual friction coefficient, with a Pearson correlation coefficient of 0.87. Increasing water content reduced interface friction through the "polishing effect". Numerical simulation results showed that the landslide remained basically stable under natural conditions. Through-going fractures greatly shortened the saturation duration of slip zones. Slope deformation exhibited a time lag of 3-13.8 h behind the rise of slip zone saturation. The overall deformation exhibited characteristics of initiation in the source zone followed by progressive transmission. The Yahuokou landslide showed an overall "front-pull and rear-push" failure mode. The strong water sensitivity of argillized carbonaceous slate slip zone soil was the internal controlling factor, seasonal heavy rainfall was the external triggering condition, and through-going fractures served as preferential infiltration channels to accelerate soil softening.

    Conclusion 

    This study quantitatively elucidates the mesoscale mechanism of water-induced strength degradation of carbonaceous slate slip zone soil and clarifies the mechanism of fracture-controlled seepage-induced instability. Zoned differentiated prevention and control measures are recommended, with priority given to sealing slope surface tensile fractures and combining drainage engineering with anti-slide support. These findings provide a theoretical basis for disaster prevention of similar creeping landslides in the Bailong River Basin.

     

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