The Development Of The Integrated Physical Model And The Analysis Of The Pollution Interception Characteristics Of Permeable Pavement In The Sponge City

With expanding of the scale of urbanization in China,the area of impervious roads increases rapidly,which leads to urban environmental problems such as urban waterlogging,groundwater shortage and urban heat island effect.Therefore,China has begun to vigorously promote the construction of Sponge City in recent years.However,in the construction process,the research on the removal effect of permeable pavement on pollutants in runoff rainwater is not sufficient,and there is not much research on whether the permeable pavement has the risk of polluting groundwater.The paper firstly developed integrated physical model of a sponge city and conducted artificial rainfall simulation demonstration to visually show the seepage velocity of runoff rainwater in the structural layer,and then proposed a assumption that the permeable pavement structure may cause groundwater pollution.In order to explore the removal condition of pollutants from the runoff rainwater by the permeable pavement system,the main experiment has selected the current two most common permeable pavement structures?the cement permeable brick pavement and the permeable concrete pavement?and the less studied cold laid and highly viscous permeable asphalt pavement structures as the research objects,By using the experiment method for the outdoor simulation of the artificial rainfall,the removal law and removal mechanism for the common pollutants?PH,conductivity,COD,NH₄⁺-N,TN and TP?in the runoff rainwater by the three kinds of permeable pavement surface layer materials under the different rainfall intensity and the removal law and removal mechanism for the pollutants by the three kinds of permeable pavement structure under the same rainfall intensity have been explored respectively,At the same time,the best permeable base layer thickness of the cement permeable brick pavement and the best permeable base layer material of the permeable concrete pavement and cold laid high viscosity permeable asphalt pavement are analyzed through the experiments,so that the theoretical guidance is provided for the concrete construction.The main conclusions of this paper are as follows:?1?With the increasing of rainfall intensity,with the increase of rainfall intensity,the removal efficiency of three permeable pavement surface layer materials on the runoff pollutants decreases gradually,and the different pollutants shows the different removal laws in the 60 min rainfall duration.The three permeable pavement surface layer materials have the best removal effect on the total phosphorus,all the average removal rate is more than 50%,the cement permeable brick surface layer and permeable concrete surface layer can significantly increase the PH value in the runoff rain water,the cold laid high viscosity permeable asphalt surface layer has the risk of the COD release.The removal laws of the three permeable pavement surface layers on NH₄⁺-N and TN are similar,and all show the trend of the slow increase after the rapid decrease and with the rainfall duration,of which,the removal rates of the cement permeable brick surface layer and permeable concrete surface layer on NH₄⁺-N and TN are much higher than that of the cold laid high viscosity permeable asphalt surface layer.?2?Under the rainfall intensity of 60mm/h,the removal rate of the three permeable pavement structures for the pollutants in the runoff rainwater shows the different regularity with the increase of the rainfall duration.The three permeable pavement structures hold the highest removal efficiency for the TP,and the removal rate is more than 70%,all the three permeable pavement structures can increase the PH value and conductivity value of the runoff rainwater,among which,the permeable concrete pavement structure is the most serious.The cement permeable brick pavement has a general effect on the COD removal,and a better effect on the NH₄⁺-N and TN removal.The permeable concrete pavement has a good removal effect on all the COD,NH₄⁺-N and TN.The removal of the cold laid permeable asphalt pavement for the COD,NH₄⁺-N and TN is poorer.The three pavement structures all have different degree of groundwater pollution risk.?3?The increasing of the permeable base layer thickness of the cement permeable brick pavement structure can improve the removal efficiency for the pollutants,but the increase amplitude of the removal rate is not significant with the increase of the thickness,the optimal permeable base layer thickness is finally determined to be between160mm-170mm through the experimental data.By comparing the influence of the permeable cement concrete base layer and permeable cement stabilized gravel base layer on the pollutant removal,it has been found that the permeable cement concrete has a better removal effect.