Seepage-related characteristics of weak interlayer suffering from a physically-chemically mediated erosion in grotto relics

The coexistence of the weak interlayer and groundwater could give rise to an undesirable geological condition, resulting in seepage-induced hazards, particularly in grotto relics. Seepage-related characteristics of a weak interlayer affected by physically-chemically mediated erosion in grotto relics were investigated. As confirmed by the morphological features, nano-indentation experiments and Raman spectroscopy analysis, the weak interlayer exhibited characteristics of disintegrability in water and low mechanical strength. The average total content of clay minerals significantly increased from 25.2 to 28.5%, compared to the pre-experimental X-ray diffraction data, despite its non-uniformity, indicating a trend toward argillization. Based on mineralogical composition, hydro-chemical data and three-dimensional morphology before and after the experiment, the changes induced by physically-chemically mediated erosion were highlighted. A coherent explanation of the permeability evolution is that the physically-chemically mediated erosion leads to the formation of fracture channel in weak interlayer under long-term water erosion and hydraulic scouring. The permeability enhanced from of 10^–7–10⁻⁸ cm/s at the initial stage to 8.01–10⁻⁴ cm/s at the existence of fracture channel.