Distribution Characteristic And Influencing Factors Of Shallow Landslide On Vegetation-covered Slope In The Loess-tableland And Gully Region Of The Loess Plateau

Land use and vegetation cover have changed greatly after implementation of the measures of vegetation restoration in the Loess Plateau.Soil erosion has been dramatically decreased,and soil and water loss have been controlled effectively.However,rainfall-induced shallow landslides occur frequently on vegetation-covered slopes on the Loess Plateau during the rainy season.However,the distribution characteristics and influencing factors of the shallow landslide on vegetation-covered slopes are still unclear.To probe this phenomenon,we conducted on-site investigations and measurements on the shallow landslides in vegetation-cover slope in the Nanxiaohegou watershed of the Loess Plateau.Frequency distribution of the characteristics of the shallow landslide on vegetation-cover slopes were calculated.Correlations were analyzed between the extension depth of the taproot of vegetation and the depth of the landslide and the erosion intensity.Differences of soil physical-chemical properties and roots distribution characteristics between upper layer(root-soil composite,Rs)and the lower layer(Ls)of the sliding surface were illuminated by sampling the typical landslide profile.The in-situ artificial simulated rainfall experiment was carried out on typical grass-covered(Artemisia gmelini slope and Wheatgrass slope),to determine the rainfall of occurrence shallow landslide,and to explore the differences of soil water content,soil indexes and root distribution characteristics in the shallow landslide profile.The main conclusions showed that:(1)The shallow landslide on vegetation-covered slope has the characteristics of group-occurring,small-scale and shallow-depth,and the erosion depth is significantly correlated with the vegetation root depth.Shallow landslide on vegetation-covered slopes are belong to small-landslide,whose length,width and depth are distributed in the range of0.5?70 m,3?31 m and 0.2?4.3 m,respectively.Slope gradient at 45°?60°is the most sensitive to the occurrence of landslides.Slope direction to the south slope,southwest slope and southeast slope is the most prone to landslides.Landslide surface type is mainly concave(57.1%).Depth of landslide shallow on different vegetation-covered type slopes is significantly different(arbor>shrub>grass).The extension depth of the taprotic roots of vegetation determines the erosion depth of the landslide,which can be expressed by a linear function(y=1.0x+10,R~2=0.82,P<0.001).(2)Differences of soil properties and root characteristics between Rs and Ls are significantly.Abundant roots are distributed in the topsoil of vegetation-covered slope,which can form typical root-soil composite(Rs),and Rs accounts for 79%of the total root density.The soil bulk density of Rs is 13%lower than that of Ls,the total soil porosity of Rs is 16%higher than that of Ls,the saturated water conductivity of Rs is 112%higher than that of Ls,and the shear strength of Rs is 46%lower than that of Ls.Those indicate that under the condition of rainfall,water infiltration of Rs is faster than Ls,and the water-holding capacity is stronger.Ls forms relative impermeable layer compared with Rs,which result in Rs gradually becomes saturated,thus inducing the occurrence of landslide.(3)Vegetation changed the flow-producing pattern on the gully-slope,and the depth of landslide was related to the soil depth where soil property and root characteristic indicators are abrupt changed.Under the rainfall intensity of 60 mm/h,there was no surface runoff on the Artemisia gmelini slope and Wheatgrass slope from the beginning of the rain to the occurrence of landslide.The cumulative rainfall of the occurrence of landslide was 185mm and 87 mm,respectively.It was accompanied by the form of interflow in the main scarp after occurrence of landslide.Landslide depth on the slope of Artemisia gmelini and Wheatgras was 21.9 cm and 43.9 cm respectively.Root quantity within the depth of 30 cm accounted for more than 80%of the total root quantity,and its distribution was dominated by fine roots(diameter<2 mm),which accounted for more than 95%.Fine roots had multiple functions between soil,root and landslide.