Study On The Storage-infiltration Effect Of The Bioretention Zone In Urban Roads

Sponge City LID measures"biological retention zone"has an important role in improving the rate of runoff control,reducing overflow pollution,and alleviating urban internal pollution.The study of its storage-infiltration effect has a far-reaching impact on the implementation strategy of future sponge city construction.Based on the analysis of the influencing factors of the storage-infiltration effect of the urban road bioretention zone,this paper determined the composition and content of the planting soil layer and filler layer,the position of pervious geotextile,the grain gradation of sand layer and thickness of structure layer as the main factors affecting the storage-infiltration effect.A total of 16 groups of orthogonal tests with 5 factors and 4 levels were used to design a combined packing experiment to analyze the influence of various factors on the storage-infiltration effects,The optimal structure of the bioretention zone under the five indicators runoff volume reduction rate,peak flow reduction rate,runoff production time,accumulated water time and soil porosity reduction rate was obtained.By simulating rainfall runoff,carrying out the storage-infiltration effect test,and using the method of intermittent inflow of clear water,the hydraulic characteristics of the bioretention zone were explored and a good fitting formula was obtained.The maximum accumulated sediment clay that the bioretention zone could undertake was obtained and assess its infiltration life.The main research results are as follows:1.Based on the experiments and numerical simulations of the storage-infiltration effect of bioretention zones at home and abroad,it was concluded that the main factors influencing the infiltration effect are:aquifer depth,area load,rainfall duration,and design rainstorm return period,Rainfall interval and air temperature,plant flooding time,structural setting,permeation rate of each soil layer,and longitudinal slope.2.Based on the principle of orthogonal test,a combined packing experiment was conducted and analyzed by extreme analysis.The order from large to small of influence of each factor on the storage-infiltration effect of the whole biological retentive zone was:the grain gradation of sand layer,composition and content of the packing layer,structural thickness,the position of pervious geotextile and the composition and content of planting soil,the grain gradation of sand layer is the most significant factor affecting the storage-infiltration effect,the composition and content of planting soil have the least influence on the storage-infiltration effect.3.According to the level of each storage-infiltration index under the five factors,the optimal level of each infiltration index was obtained.Finally,the optimal structure of the bioretention zone was:the thickness of the planted soil layer is 200mm,and its composition sand,peat and clay The content is 75%,20%and 5%;the thickness of the filler layer is350mm,the content of its constituent sand,loam,vermiculite and perlite is 75%,10%,5%and 10%;the sand thickness is 100mm,and the particle gradation is For 0⁰.5mm accounted for 15%,0.5⁰.7mm accounted for 40%,0.7¹mm accounted for 30%,1²mm accounted for 15%;gravel layer thickness 200mm;do not add pervious geotextile.4.Based on the bioretention zone of optimal structure,a study was conducted on the storage-infiltration effect.The total effluent with a 5 g/L influent clay concentration was 1/3of 20 g/L,and the cumulative water output and time presented a power function relationship V=atb.More than 75%of the power function is better than 0.99.As to the influent clay concentration of 5g/L and 10g/L,The clear water rinsing effect delays the peak appearance time by 9min and 5min,As to the influent clay concentration of 15g/L and 20g/L,it advanced the peak appearance time by 9min and 5min.and the clear water rinsing effect can reduce the outflow peak.5.The time-dependent curve of permeation rate in this experiment can be fitted with Horton model,Kostiakov model,and general empirical model.The general empirical model f=m+nt^-?has the best fitting effect,and the correlation coefficient R² is almost above 0.9997.Secondly,the better fitting effect is the Kostiakov model f=at^-b,the correlation coefficient R²is 0.9942,and the Horton model f=f_c+?f_o-f_c?e^-?t has a poor fitting effect,and the correlation coefficient R² is 0.9644.6.The total reduction rate of rainwater runoff in the different accumulated sediment volume bioretention zone was 1.77%to 59.04%.The runoff reduction rate of clear water inflow was positively correlated with the accumulated clay content.The runoff reduction rate of muddy water inflow was negatively correlated with the accumulated clay content.The peak flow reduction rate in the different accumulated sediment volume bioretention zone is 87%⁹7%.With the increase of accumulated clay,the peak discharge rate decreases,the peak flow reduction rate increases,and the peak discharge rate is inversely proportional to the cumulative amount of deposited clay.The peak flow reduction rate is proportional to the cumulative amount of deposited clay,and this relationship can be well linearly fitted.7.With the increase of accumulated clay content,runoff production delay also increased,and the maximum duration of the runoff was 65.72 min.The accumulated water time increases with the increase of accumulated clay content.The maximum water accumulation time is 7.8h which is 21.5 times of the minimum water accumulation time.The necessary emptying time for plant growth is 24⁴8h,and the depth of accumulated water is the highest about 175mm.The soil porosity reduction rate decreases with the increase of accumulated clay content.The initial soil porosity reduction rate is only 3%,and the total settlement is only 2.5cm.8.The domestic relevant regulations show that bioretention zone system has a permeability coefficient of not less than 10^-5m/s.When the accumulated clay content in the bioretention zone reached 1.126kg,the clay load was 4265.15kg/hm².As for area load is 10times of itself,rainfall duration is 10min and design rainstorm return period is 2 years,It takes 3 hours to emptying such a flow.The permeability coefficient was only 0.98×10^-5m/s,the permeation effect is so poor that can not satisfy the originally designed use function.When the cumulative amount of deposited clay reached 1.877kg,water accumulation time was even 7.8h.Take Jiaoda road of Chengdu as an example.According to Lu Xiongfei's research on the characteristics of rainwater pollution at the beginning of a road,for a year's rainfall,if the SS pollution load value is 202.98kg/?hm²·a?,then the bioretention zone's life expectancy is about 21 years.