| To investigate deeply the hydrological effects of plants in the loess area of the Xining Basin and the principles of plant protection,four dominant herbs-Elymus sibiricus Linn.,Elymus nutans Griseb.,Agropyron trachycaulum Linn.Gaertn.,Achnatherum splendens(Trin.)Nevski and four dominant shrubs of Caragana korshinskii Kom.,Nitraria sphaerocarpa Maxim.,Zygophyllum xanthoxylon Bunge Maxim.,Lycium barbarum L.were selected as the test subjects at the self-built Changlinggou catchment in Xining basin.Two slopes were designed to be straight-shaped and step-shaped respectively.Then,the growth characteristics of 4herbs and 4 shrubs were compared in different growth periods.The physical and mechanical properties of unvegetated bare slope and vegetated slope were tested and analyzed.The characteristics of runoff,sediment yield and infiltration on the slope were studied through artificial rainfall simulation tests under the condition of different herbs and slope shapes for artificial rainfall simulation tests.The main influencing factors of slope infiltration were discussed by Pearson correlation analysis method.Three kinds of models,Kostiakov model,Horton model and general empirical model,were used to simulate the soil infiltration process of slope,and the soil infiltration models suitable for six types of slope were analyzed.Finally,through the finite element numerical simulation method,the deformation and failure characteristics of the six types of slope under different herbs and slope shapes were discussed,based on the limit equilibrium method,the stability of the six types of slope in test area was evaluated.Through the above research,the main results are as follows:(1)According to the simulated rainfall test,compared with the unvegetated slope,the cumulative runoff and cumulative sediment yield of the slopes planted with Elymus nutans Griseb.and Elymus sibiricus Linn.are the smallest,the values are51.42 L,51.25 L,160 g,210 g respectively.Compared with straight-shaped slope,the cumulative runoff and cumulative sediment yield of the step-shaped slope planted with Elymus nutans Griseb.is relatively small,the values are 5.62 L,110 g,further analysis showed that,compared with the straight-shaped slope,the cumulative runoff and cumulative sediment yield decreased by 89.07%and 31.25%for the step-shaped slope of Elymus nutans Griseb,which shows that step-shaped slope can effectively reduce the runoff.(2)Further analysis of the simulated rainfall test showed that the infiltration rate of the slopes planted with Elymus nutans Griseb.and Elymus sibiricus Linn.are relatively large,the values are 0.38?0.44 mm/min.Compared with straight-shaped slope,step-shaped slope can effectively extend the soil moisture infiltration time on the slope surface and reduce the runoff,the infiltration rate of the step-shaped slope planted with Elymus nutans Griseb.are relatively large,the values are 0.50?0.52mm/min.The further study showed that compared with the bare slope,the infiltration rate of the step-shaped slope planted with Elymus nutans Griseb.increased by52.94%?85.19%.(3)According to Pearson correlation analysis results,there is a significant positive correlation between soil organic matter and initial infiltration rate(R~2=0.986),and a very significant correlation between vegetation coverage and stable infiltration rate(R~2=0.997).And three infiltration models were selected to fit the infiltration process of soil water of six types of slopes.It can be seen that in straight-sloped slope,the fitting effect of Horton model and general empirical model is relatively significant for soil infiltration process of four types of slopes.Accordingly,the fitting effect of Horton model is the best for the soil infiltration process of step-sloped slope.(4)The results of the finite element numerical simulation show that the bare slopes have relatively significant horizontal and vertical displacement changes than the vegetated slopes after simulated rainfall in test area.Compared with the bare slope,the horizontal and vertical displacements of the three herb slopes planted with Elymus nutans Griseb.,Elymus sibiricus Linn.and Agropyron trachycaulum Linn.Gaertn.decreased by 25.88%?52.94%and 0%?23.04%,respectively.And with the increase of rainfall duration,planting herbs can effectively reduce the slope maximum shear stress concentration area,and the maximum shear stress concentration area of planting Elymus nutans Griseb.is the smallest in the straight-shapped slope,with the value is0.396 m~2.Furthermore,compared with the straight-shaped slope,the maximum shear stress concentration area at the bottom of the step-shaped slope after the simulated rainfall are relatively small,and the maximum shear stress concentration area of the step-shaped slope planted with Elymus nutans Griseb.is 0.226 m~2,so the stability of the step-shaped slope is relatively significant.(5)The limit equilibrium method was used to calculate the safety factors of six types of slopes in test area,it can be seen that Elymus nutans Griseb.and Elymus sibiricus Linn.have the most significant effect on slope stability.When the simulated rainfall lasted for 60 min,the safety factor of the slope planted with Elymus nutans Griseb.is the highest at 1.813,the second is the slope of planting Elymus sibiricus Linn.,and its safety factor is 1.783.Compared with the straight-shaped slope,the slope stability of the step-shaped slope is more significant,when the simulated rainfall lasted for 60 min the safety factor of the stepp-shaped slope planted with Elymus nutans Griseb.is 2.151.(6)According to the shear strength index evaluation method,compared with the bare slope,the shear strength of the slope planted with Elymus nutans Griseb.and Elymus sibiricus Linn.is the largest,and the cohesion increases by 51.12%and52.46%,respectively.Similarly,compared with the straight-shapped slope,the shear strength of the step-shaped slope is significantly enhanced,and the cohesion value of the step-shaped slope planted with Elymus nutans Griseb.is 12.66 k Pa.Further research shows that the results obtained by the shear strength index evaluation method are basically consistent with the calculation results obtained by finite element numerical simulation in this research.The results of this study have a theoretical value and practical significance in further adopting plants to carry out slope protection,and effectively preventing and controlling regional soil erosion,shallow landslide and other geological disasters. |
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