| The sunken greenbelt is an important facility for the source governance of road rainwater runoff and runoff pollutants in the construction of sponge city.It has the characteristics of strong applicability,good landscape and stable runoff control effect.At present,the design parameters of the undercut green belt in Wuhan and its control effect on the runoff and runoff pollutants have not been detailed and reliable,and relevant experimental research is needed to guide the engineering design,operation and maintenance.Through the rainfall simulation experiment,the effects of the sunken greenbelt with different packing layer soil and sand ratio on the rainwater runoff and runoff pollutants were studied,and the rainfall return period,rainfall duration,pollutant concentration to storm water runoff and runoff pollution experiment and analysis of the control effect of the object,the experimental conclusions are as follows:?1?The use of medium coarse sand and soil layered by volume ratio can significantly improve the sunken greenbelt.The permeability coefficient of each packing layer with soil-to-sand ratio of 8:22:8 is 8.93×10-66 m/s1.98×10-55 m/s,which meets the penetration ability of 24 h emptying and soil water retention.?2?When the soil-sand ratio of the packing layer is 8:2 and 6:4,the sunken greenbelt has the best control effect on the runoff.Under the conditions of each rainfall return period,the 8:2 structure with soil-to-earth ratio can control the total annual runoff of 65.8%70.9%in Wuhan.When the rainfall duration t=60 min,the critical rainfall of each soil-soil structure is 18.30 mm23.29 mm.When the rainfall duration t=120 min,the soil-sand ratio structure can store 15.60 L/m221.75 L/m2 runoff.The peak reduction ratio of the soil-to-sand ratioof 8:2 and 6:4 in the packing layer is 22.74%49.82%,and the peak reduction rate increases with the duration of rainfall.?3?The effect of different soil-sand ratios on the pollutants is gradually reduced with the design return period and the concentration of pollutants.It increases with the duration of rainfall,and the residual pollutants appear in the early stage of the runoff.The different structures of soil-sand ratio have good effects on runoff SS,NH3-N and TP.The total reduction rate is 76.63%88.23%,69.04%90.20%and 83.09%91.28%when P=10a rainfall,the influent concentration has a significant effect on the reduction of NH3-N,TP,and TN in the sunken greenbelt,and has little effect on the SS reduction effectand the COD reduction effect.The structure with high proportion of soil volume in the packing layer has better effect on reducing the runoff pollutants,and the quality of the runoff water can reach the discharge standard of urban sewage plants.?4?It is suggested that the typical undercut green belt in Wuhan should be improved by medium coarse sand.The ratio of soil to sand should be 8:2 and 6:4.The structure of the undercut green belt is from top to bottom for the storage layer,plant and packing layer300.Mm,gravel drainage layer 300 mm. |
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