Experimental Study On Anti-Erosion Performance Of Frost Resistant Vegetation Concrete Ecological Slope Protection

With the gradual promotion of national construction of life community of mountain,water,forest,field,lake,grass and sand,ecological protection of river slope has become a hot research topic.The ecological protection of river slope needs not only to ensure the long-term stability of the slope,but also to create a good ecological and green environment for the people.As a new type of slope protection with dual functions of engineering protection and ecological construction,anti-freeze vegetation concrete ecological slope protection has broad prospects in the application of ecological slope protection,and it is of great significance to study its anti-scouring performance.On the basis of the research conducted by the research group,we will conduct in-depth experimental research on the anti erosion performance of frost resistant vegetation concrete ecological slope protection.Firstly,prepare freeze-resistant vegetation concrete test blocks for physical and vegetation performance testing research;Secondly,a set of flume channel models simulating natural river channels was designed and developed,and three different levels of anti freezing vegetation concrete ecological slope protection were conducted,including water flow velocity（0.4m/s,0.8m/s,1.2m/s,1.6m/s,2.0m/s）,erosion duration（0.5h,1.0h,1.5h,2.0h,3.0h,4.0h）,and vegetation planting period(1month-C₁,1.5months-C_1.5).The same type of grass planting slope protection（garss period 1month-G₁）and plain soil slope protection（S）erosion tests were conducted,Study the effects of various factors on the bed shear stress and scour depth of slope protection samples,and explore the anti erosion performance of frost resistant vegetation concrete ecological slope protection;Then,conduct shear performance tests on C₁,C_1.5,G₁,and S slope protection samples to study the mechanism of ecological slope protection’s anti erosion performance;Finally,the research results will be applied in engineering demonstration.The main conclusions are as follows:（1）The average compressive strength of antifreeze vegetation concrete blocks for 28d can reach 15.2MPa with an average porosity of 23.5%;The p H of concrete pore liquid can be reduced to 8.2 after treatment with composite alkali-reducing solution.In the planting test,mixed turf of Tall Fescue and premature bluegrass is selected.The grass grows well and can grow to 20 cm after 21 days of maintenance.At 30 days,the grass roots can penetrate the concrete slab and penetrate into the bottom soil.（2）Based on the design flow rates of 0.4m/s,0.8m/s,1.2m/s,1.6m/s,2.0m/s and the scouring resistance test requirements of C₁,C_1.5,G₁ and S slope protection,a set of channel model for simulating natural river channel and a sample box for simulating slope protection are designed and developed.（3）Under the same scouring time,with the increase of flow rate,the bed shear stress of C₁and C_1.5 slope protection shows an exponential upward trend.At the maximum flow rate,the shear stress is 65.42Pa and 84.34Pa respectively.The depth of scouring pit gradually increases with the maximum flow rate of 16mm and 12mm respectively.At the same flow rate,with the increase of scouring time,the bed shear stress of C₁ and C_1.5 slope protection shows a trend of more decrease in the early stage and less decrease in the later stage until it is stable.The scouring depth shows a trend of increasing more in the early stage and rising less in the later stage until it is stable.Under the same flow rate and scouring time,the bed surface shear stress C_1.5>C₁,the scouring depth C_1.5<C₁,and the scouring resistance C_1.5>C₁.（4）At the same planting period and scouring time,with the increase of flow rate,the bed surface shear stress G₁>C₁,scouring pit depth G₁<C₁,and the scouring resistance of G₁ slope protection is greater than that of C₁ slope protection.At the same flow rate,the scouring depth of S slope protection is much greater than that of C₁ slope protection and G₁ slope protection.At 1.2m/s,the scouring depth of C₁ slope protection is 8mm.At the same flow rate,the scouring depth of S slope protection is 40mm.C₁ slope protection can reduce 80%of soil loss and show good anti-scouring performance.At the same flow rate,with the increase of flushing time,the bed shear stress value C_1.5>G₁>C₁,the depth of scouring pit value S>C₁>G₁>C_1.5,and the anti-scouring performance is C_1.5>G₁>C₁>S.In the scouring failure test,when the limit scouring time of S slope protection reaches 0.5h at 2m/s,it will be seriously damaged.The limit scouring time of C₁,C_1.5 and G₁ slope protection is 8.5h,9h and 8.5h respectively,and the scouring pit depths are 40mm,35mm and 45m respectively.The scouring resistance is C_1.5>C₁>G₁>S.（5）Linear regression model and Coulomb strength formula for shear strength of C₁,C_1.5,G₁ slope protection root-soil complex and S slope protection rootless soil samplesτ=σtanφ+c is consistent with the Moore-Coulomb failure criterion.The shear strength of three kinds of ecological slope protection soil is significantly higher than that of plain soil.The main reason is that vegetation roots in ecological slope protection have certain reinforcing effect on soil,which can effectively improve soil cohesion and shear strength.The order of soil shear strength is C_1.5>G₁>C₁>S.（6）The research results were applied to the ecological slope protection project of upstream and downstream of Nanjing Luyihe Bridge.The anti-freeze vegetation concrete ecological slope protection vegetation grew well and the slope coverage rate reached over 95%after 28d.After five floods in a flood season,the concrete ecological slope protection with antifreeze vegetation is safe and stable.The maximum scour pit depth of the vegetation layer is 30mm.The vegetation slope protection is moderately damaged.The vegetation will resume normal growth after 5 days.The results show that the anti-freeze vegetation concrete ecological slope protection has good anti-scouring performance.This subject studies the anti-scour performance of anti-freeze vegetation concrete ecological slope protection and carries out engineering demonstration application,which provides theoretical support for the wide application and promotion of anti-freeze vegetation concrete ecological slope protection and has certain value and significance for promoting the construction of ecological civilization.