| Gravity erosion on gully slope is an important component of soil loss on the Loess Plateau. The research of gravity erosion process has four outstanding difficulties:difficult to observe, difficult to test, difficult to model and difficult to verify. By analyzing and comparing the gravity erosion test results of rainfall simulation experiments on the indoor and field loess gully model, the gravity erosion in the Loess Gully Slope were classified and the sensitivity of influence factors were quantified. The main studying contents are as follows:(1) The development process of gravity erosion in gully slope is deeply explored. Based on the movement mechanism of gravity erosion, moisture content and accumulation, the gravity erosion triggered by rainfall in the Loess Gully Slope is divided into landslide, collapse and mud. As the slopes were eroded with five runs of rainfalls each at an amount of 48 mm, the total volume of avalanche, landslide, and mudslide were 150.9,82.5, and 3.9×103cm3/m, and their maximum individual amounts were 136.4,71.1 and 5.1×103cm3, respectively. The amount of avalanche, landslide, and mudslide accounted for 62,36, and 2% of the total gravity erosion in a rainfall experiment of the model test. The experiment results show that the quantity of soil loss caused by avalanche and landslide was much more than that caused by mudslide, and the avalanche was the most violent gravity erosion. As a result, avalanche and landslide, especially the former, played a crucial role of soil erosion on steep slope compacted by hand with loess.(2) The increase-rate-analysis method presented by the authors was used to evaluate variations in the gravity erosion with respect to changes in other causal parameters of rainfall duration-intensity and slope height-gradient. Climate-driven factors and topography triggers had prominent influences on gravity erosion. With the increase of rainfall intensity, rainfall duration, slope gradient and slope height, the total amount and the maximum single amount of gravity erosion are also increased in most cases. Whether for the total amount or the peak amount in an experiment, the largest sensitivity parameter on both landslides and mudslides was that of rainfall duration. In comparison, topography was relatively less influential. For the total amount in an experiment, the sensitivity parameters of rainfall duration on the landslide and mudslide were 24.9 and 19.5, respectively, while the sensitivity parameter of rainfall intensity on the avalanche was 2.2. For the peak amount in an experiment, the sensitivity parameter of rainfall duration on the landslide and mudslide were 5.5 and 15.6, respectively. Meanwhile the sensitivity parameter of slope gradient on the avalanche was 4.6.(3) With the same initial terrain, initial water content and rainfall conditions, the gravity erosion trigger forms, the gravity erosion accounted for the total erosion ratio and various types of gravity erosion in the proportion are relatively similar in the model testing and field tests. This is due to the soil types of field tests and model tests are both sandy loam and their dry densities are very close, their soil moisture distributions are also similar, and when the soil moisture content is close to saturated soil structure strength greatly weakened.(4) The scale and amounts of gravity erosion in the model test are much larger than that in the field test, this is due to the initial soil hardness in field test is about three times of model test, and soil water content is slightly less than that of the model test. For the soil hardness is a comprehensive index reflecting soil shear strength and infiltration rate of soil and experimental observation showed that there are significant relationship of soil hardness and erosion. Furthermore, when the initial hardness of the soil increased 1.97 times, the soil gravity erosion increased by 2.35 times. |
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