Design Optimization And Control Effect Simulation Of Drainage System Of Permeable Pavement Road In Sponge City

With the rapid development of urbanization in China,the impervious area such as urban roads continues to increase,and non-point source pollution such as urban stormwater runoff brings great harm to the ecological environment.To this end,based on LID?Low Impact Development?technology,China proposes the construction concept of“sponge city”,through the coupling of gray infrastructure anad green ecosystem,and maximizes the sponge effect of urban roads,which not only allows traditional roads to play the role of infiltration and retention,but also effectively reduces runoff pollutants through green ecosystems.This paper expounded the runoff generation mechanism of urban permeable pavement,and combined the Ranieri model to optimize the design of the drainage permeable pavement drainage system.Constructing a gray-green combined drainage system with superficial drainage type,base storage and drainage type and full-transparent permeable pavement and green ecological ditch,and reasonably determined the drainage system structural parameters of gray-green combination.The data road of Xi'an New District was selected as the test section.The gray-green combined drainage system coupled with the surface drainage type permeable asphalt pavement and the green ecological ditch was constructed,and the optimal drainage capacity of the drainage system was derived.Based on the reappearance period of the rainwater pipe design,a new concept is proposed—the reappearance period of the permeable asphalt pavement design.The diameter of the longitudinal water collection pipe in the permeable asphalt pavement was 100mm,and the three rows of orifices with a hole diameter of 5mm were arranged at equal intervals,and 36 holes were arranged per row per row.The horizontal drain pipe had a pipe diameter of 100 mm and a spacing of 20 m.The road adopted rectangular curb stone with the width of 0.1 m and the height of 0.15 m,and the opening pitch was set to 25 m.The inner diameter of the perforated water collecting pipe at the bottom of the green ecological ditch was 100mm,the opening hole diameter was 12mm,the hole center distance was 150mm,the uniform opening was 3 rows,and the overflow rectangular shape was at least 85mm×85mm.The design of the municipal rainwater pipe is600mm,the flow rate inside the pipe is 1.38 m/s,and the slope of the pipe bottom is 3.9‰.Through SWMM software,the control effect of the coupling system of permeable pavement and green ecological ditch on hydrological and water quality were simulated under the repetition period of 2,5,10,20 and 50 years.The results showed that when the recurrence period increased from 2 to 50 years,the runoff generation time of the coupling system was significantly delayed compared with the current situation,and the peak runoff occurrence time was delayed by 5 minutes.The reduction rates of peak runoff were 70.6%,54.2%,46.6%,40.6%,36.6%,and the runoff coefficients were 0.40,0.59,0.68,0.77 and 0.87,respectively;The coupling system had a good control effect on the concentration of TSS,COD,TN and TP in surface runoff pollutants.Under the condition of low recurrence rainfall,the coupling system reduced the pollutants TSS,COD,TN and TP by 87.12%,87.68%,89.17%and89.77%.Through the finite element analysis of the coupled system of the permeable asphalt pavement and the green ecological ditch,the laboratory constructed a test model of the combined unit of the permeable asphalt pavement mixture and the bioretention tank,and carried out artificial rainfall test.The purification effect of the permeable concrete asphalt mixture and the bioretention cell combination unit on the pollutants was studied.The results showed that after the purification of permeable asphalt pavement mixture and the bioretention tank,the average removal rates of pollutants SS,COD,NH₄⁺-N,TN,TP,Pb²⁺and Cr⁶⁺were94.82%,83.40%,68.21%,51.32%,63.65%,100%,89.67%respectively.Subsequently,the effects of rainfall intervals of 4,7,14 and 21 days on pollutants purification were studied.The results showed that the rainfall interval increased from 4 days to 21 days.The removal rates of SS and NH₄⁺-N remained stable.The removal rates of Pb²⁺and Cr⁶⁺increased.The removal rates of TN,TP and COD decreased.Among which TN was the most affected by rainfall interval,and the removal rates decreased from 73.55%to 14.52%.