Erosion Decomposition and Microscopic Characteristics of Weakly Cemented Pebble-cobble Mixed Soil

Weakly cemented pebble-cobble mixed soils are widely distributed in southwestern China. These materials characterized by low diagenetic maturity, weak cementation, and pronounced susceptibility to softening and disintegration, present substantial risks to slope engineering. This study presents a systematic investigation of six representative soil types from the Zhala hydropower station area in Tibet. An integrated methodological approach was employed, incorporating chemical analysis, dissolution tests, wet-dry cycling disintegration experiments, and scanning electron microscopy (SEM). The research focuses on elucidating the chemical composition,, dissolution and migration patterns, and microstructural evolution under hydro-chemo-mechanical interactions. Key findings include: (1) The soils are generally weakly alkaline, with the exception of calcareous cemented types, contain abundant soluble salts (predominantly SO₄^2- and Cl⁻. SO₄^2- serves as a primary indicator of dissolution, with both surface water and groundwater immersion significantly enhancing the leaching of soluble salts, particularly SO₄^2- and Ca²⁺... Calcareous-cemented soils exhibit relatively higher resistance to erosion.. (2) Wet-dry cycles exert a pronounced influence on disintegration behavior, with the initial cycles causing the most substantial structural deterioration. Soils with high initial porosity demonstrate the greatest susceptibility to disintegration. While cementation type and structural integrity play a critical role in mitigating, specific spatial configurations of cementation and pore distribution may result in synergistic degradation, thereby amplifying disintegration potential.. (3) Water saturation leads to progressive microstructural deterioration, wherein stable, dense fabric (characterized by face-to-face particle contacts) transitions to a loose, porous arrangement (dominated by edge-to-edge and point contacts). This transformation is accompanied by particle rounding, crack propagation, increased porosity, and enhanced pore connectivity. The most significant degradation is observed in samples with weak cementation and localized pore development. These findings contribute to a deeper understanding of the hydro-chemo-mechanical mechanisms governing the behavior of weakly cemented pebble-cobble mixed soils and offer valuable theoretical and practical insights for slope stability assessment and engineering design in similar geological settings.