Formation process and connectivity of sliding zone soil of Huangtupo landslide in the Three Gorges Reservoir area

ObjectiveThe characteristics of sliding zone soil play an important role in landslide stability and activity, and are also essential factors for effective landslide prevention and control. Existing research on sliding zone soil primarily focuses on physical stability assessments, including monitoring of sliding mass displacement, whereas limited studies explore the chemical characteristics of sliding zone soil, especially sliding zone clay. MethodsTo address this gap, a comprehensive analysis of sliding zone soil samples from the Huangtupo landslide was conducted using X-ray powder diffraction (XRD), X-ray fluorescence spectroscopy (XRF), Mössbauer spectroscopy, and magnetic susceptibility. ResultsThe results revealed that intense water-rock interactions in the sliding zone led to the dissolution of calcite and the formation of clay minerals. These processes caused a loss of Ca and the relative enrichment of Si, Al, and Fe, resulting in continuous deposition and aggregation of clay minerals in the sliding zone, and formed a typical strip-shaped or nest-like sliding zone soil. The sliding zone soil was enriched in Fe3+ but depleted in Fe2+, indicating a relatively strong oxidation environment. This suggested that the sliding zone had good connectivity with the surroundings, and the water in the sliding zone and the external water (especially the infiltration of surface water) might be in a relatively smooth and stable circulation state. Therefore, the ${\rm{Fe}}^{{3+}}/\Sigma {\mathrm{Fe}} $ ratio of sliding zone soil can be used to indicate the connectivity and chemical stability of the sliding zone. The higher the magnetic susceptibility of the sliding zone soil, the higher the corresponding Fe3+ content, and the better the connectivity of the landslide, indicating that the landslide is more stable. Based on the results of magnetic susceptibility and total iron content of the samples, an empirical formula $ {\text{Fe}}^{\text{3+}}/\Sigma{\text{Fe}}=(\chi +1.059)/{\text{2.414}}w(\text{T}{\text{Fe}}_{\text{2}}{\text{O}}_{\text{3}} $) is proposed. This formula enables a quick calculation of the ${\rm{Fe}}^{{3+}}/\Sigma {\mathrm{Fe}} $ ratio of the sliding zone soil to identify the redox environment and evaluate the connectivity and stability between the sliding zone and the surrounding environment. This approach enhances the timeliness of landslide risk assessments. ConclusionThe research results provide a new basis for landslide stability evaluation.