Abstract: Preferential channels such as large pores exist in actual slope soil where the water movement exhibits preferential flow characteristics. In this paper, we conducted a rain staining tracer test on undisturbed soil columns to investigate the development characteristics of large pores in natural slope soils and the spatial response rule of preferential flow under the action of rainfall. By calibrating the water infiltration area using staining information, we evaluated the influence of the development characteristics of different large pores inside the soil column on the development of preferential flow and water infiltration flux according to the parameter “water infiltration area ratio”. The research results revealed strong development and spatial variability of preferential channels in the undisturbed soil column. The preferential channel types are mainly large pores. To be specific, in large pores with good connectivity and opening degree, the preferential flow passes quickly, with weak exchanges with the surrounding matrix, hence replenishing groundwater quickly in large quantities; in large pores with irregular distribution and different directions, the preferential flow is weakened with strong exchange with matrix which yet gradually weakens with depth; in some dead-end large pores which retain more water, the water exchange with the surrounding matrix is enhanced, which is of little help to the migration of preferential flow. The results of the dyeing tracing evaluation are completely consistent with the laws obtained from the measured soil water fluxes of the soil column, which accurately reveals the typical spatial distribution characteristics of large pore flow in undisturbed soil.

Key words: preferential flow, large pore, preferential channel, dyeing tracer, undisturbed soil column