Study on the dominant infiltration characteristics of unsaturated fissure soil under different rainfall conditions

This paper simplifies the rainfall infiltration in expanding soil landslide into a vertical slope soil column model. Utilizing the basic theory of the Richards equation and based on a discrete pore-fracture medium model, combined with two typical rainfall conditions of short-term heavy rainfall and long-term light rainfall, with different fracture depths as the main variable, the study explores the preferential flow infiltration characteristics during the development and evolution of fractures from the dominant permeability, saturation profile, permeability rate, surface pressure, and permeability in the development of permeability characteristics. The results show that, (1) at the fissure, the rainfall forms a temporary saturation area at the end of the fissure, then horizontally infiltrates to both sides of the fissure, with the saturation mode being bottom-up. at non-fracture sites, rainfall mainly vertically infiltrates along the soil column surface, with the saturation mode being top-down.(2) Under short-term heavy rainfall, with the increase of fissure depth, the dominant flow controls the process of rainfall infiltration. The infiltration amount and infiltration depth are directly proportional to the fissure depth, and the infiltration depth is basically consistent with the fissure depth.(3) Under long-term weak rainfall, the infiltration effect of dominant inflow is weakened, and the phenomenon of dominant flow is slow. The infiltration speed of rainfall along the fissure is basically the same as that of the matrix pore, and the infiltration is mainly manifested as vertical infiltration downward along the surface of the soil column.