Permeability variations of two types of soils (G1 soil with high dispersibility

G2 without) from debris flow source area in Jiangjiagou ravine (Yunnan province) due to fine particles transport were evaluated under constant head condition (the constant pressure head is 5 cm) in soils column. Boiled tap water and suspension of 1 g/L particles (the size range: 1.6－104.74 μm) was successively used as inflow water for both soil column experiments. During the stage of boiled tap water seepage flow

permeability coefficient of both the soil layers near the inlet of the column decrease

while that of both the soil layers near the outlet of the column first increased

then decreased. During the stage of particles suspension seepage flow

permeability coefficient of both the soil layers along the column decreased; and the most severe decreases of permeability occurred near the inlet of the columns. The permeability coefficient of soil G1 reduced by more than one order of magnitude; the permeability coefficient of soil G2 reduced by about two orders of magnitude; and the amount of time spent reaching those values in soil G2 was less than in soil G1. That is the rate of the decrease of permeability coefficient in soil G2 was more than in soil G1. Flow rate for both soils significantly decreased in this stage. The results show that the dispersion played a leading role in the seepage process. In other words

the process of itself particles release and transport can affect the pore concentration and offset the clogging effect induced by the deposition of the foreign particles. After the experiments

the pore space of both the soil layers near the inlet of the columns were almost filled by the foreign particles

and the filling rate gradually decreased along the column by observed with the naked eye

which was in agreement with the results of the permeability coefficient decrease of the soils along the column. In addition

the mass loss of particles only occurred in the first several tens of minutes

and the sizes of the loss particles from the two soils fell within the same range of 1–100 μm