In order to study the chatacteristics of different soil erosion and sediment yield indoor and outdoor under rainfall condition

the erosion processes of Mangshan mountain loess were tested under laboratory and undisturbed conditions on 25°steep slopes under artificial simulated rainfalls.The similarity characteristics of the indoor and outdoor process of erosion and sediment yield were analyzed by the fuzzy closeness degree calculation method.The results show that with the rains of same intensity

runoff amount

sediment concentration

shear stress

and sediment yield of different soil bulk densities were fairly low at the initial stage and increased gradually over time;when the rain intensity reached the hyperplastic spot

these indicators increased sharply to the steady state within a few minutes.On 25°steep slopes

the nearness degree of the shear strength

runoff rate

sediment concentration and sediment yield of both indoor and outdoor simulation were very similar for the two kinds of soil bulk densities.The nearness degree of the high bulk density(1.2 g/cm3)soil was greater than the low bulk density(1.0g/cm3)soil.This implies that in order to achieve a laboratory condition similar to the field condition

the soil with higher bulk density should be applied in the simulations.