| In order to make a study of law of soil erosion in the process of expressway construction and have a definite object in view to adopt appropriate soil and water conservation measure system, this paper takes expressway soil erosion as research object and chooses the expressway from Yichang to Changyang situated in west region of Hubei provinces as an example to analyse expressway soil erosion characteristic and influencing factor, impact of highway soil erosion on ecological environment and law of soil erosion occur and development in side slope of expressway.According to the research the soil and water conservation comprehensive measures system of expressway is raised and it contributes to distribution of soil and water conservation measures of similar highway as a reference.(1) In the process of expressway construction soil erosion quantity has intimate relation with rainfall, soil and vegetation. Through analyses conclusion can be drawn as below. In the corresponding period the result of comparing soil erosion quantity of each observation plot showed that maximal soil erosion had occured in dumping ground slope. The soil erosion of frame girder plot and road embankment slope is fewer, and the soil erosion of vegetation resumed plot is the least.(2) In a good many rainfall factor, major rainfall factors affecting soil erosion quantity were rainfall and antecedent rainfall quantity and there was a notable positive correlation betwween them; Through multiple regression analysisthe, regression equations can be drawn for soil erosion quantity(Y/kg·m-2) and rainfall (X1/mm) and antecedent rainfall quantity (X2/mm) .The regression equations are as the following:Dumping ground 1 without vegetationY1=0.989X1 +0.017X2 ( X1 5≥10.3, X2 ≥0.58) Dumping ground 1 without vegetationY2 =1.107X1+0.126X2 (X1≥14, X2≥0) Road embankment slope 1 with vegetationY3 =0.985X1+0.005X2 (X1≥10.5, X2≥0) Road embankment slope 2 without vegetationY4 = 0.900X1 + 0.086X2 (X1≥10.5, X2≥0) Frame girder plot 1 with yellow loamY5 =0.887X1+0.110X2 (X1≥16.4, X2≥0) Frame girder plot 2 with red loamY6 = 0.891X1 + 0.085X2 (X1≥16.4,X1≥0)(3) The soil erosion quantity and the soil gravel content are just related, the gravel content is more high in the soil grain, soil grain the hole of more big, under the situation that have rainfall, the small grain in the soil more easy flow along with the runoff.(4) Vegetation plays an impotant role in reducing soil erosion quantity of dumping ground in the process of expressway construction. In research expressway different kinds of mix-seeding vegetation showed a remarkable impact on soil erosion: Pattern of mix-seeding vegetation of grass, frutex and arbor had a best effect on reducing soil erosion and pattern of mix-seeding of grass and frutex took second place and pattern of mix-seeding of grass took the last. Besides different pattern of vegetable mix-seeding, plant species had a strong impact on soil erosion. At present in the mix-seeding pattern of grass and frutex Testuca arundinacea +Festuca rubra + Cajanus fulvus DC. + Tephrosia Candida (Roxb.) DC. + Crotalaria pallida Ait. had a best effect on reducing soil erosion. In the mix-seeding pattern of grass, frutex and arbor Testuca arundinacea+Festuca rubra+Indigofera pseudotinctoria Mats. +Lespedeza+Alnus+Robinia pseudoacacia L. had a strong adaptability to research expressway and a best effect on reducing soil erosion.(5) Gully erosion is serious in the experimental area, of which the amount of detritus erosion can reach 92848t/km2. It is found the erosion length is almost within 40cm, which is increasing from the top slope to the bottom slope based on the size of the catchment are.(6) The controlling measures of highway soil erosion shoule be arranged in accordance with lawof occuring and development of expressway soil erosion and guiding principle of "prevention first, prevention and cure incorporation" should be carried out throughly in arranging all kinds of soil and water conservation measures.
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